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Full text of "Evaluation of aerial remote sensing techniques for defining critical geologic features pertinent to tunnel location and design"

y 



Technical Report Documentation Page 



1. Report No. 



FHWA-RD-76-72 



2. Government Accession No. 



3. Recipient's Catalog No. 



vV 



4. Title and Subtitle 



Evaluation of Aerial Remote Sensing Techniques 
for Defining Critical Geologic Features 
Pertinent to Tunnel Location and Design 



5. Report Date 

March 1976 



6. Performing Organization Code 



7. Author's) 



8. Performing Organization Report No. 



0. Russell, D. Stanczuk, J. Everett, R. Coon 



9. Performing Organization Name and Address 

Earth Satellite Corporation (EarthSat) 
7222 47th Street, N.W. 
Washington, D.C. 20015 



10. Work Unit No. (TRAIS) 

35B2-022 



11. Contract or Grant No. 

DOT-FH-1 1-8598 



12. Sponsoring Agency Name and Address 

U.S. Department of Transporta tion 



Federal Highway Administratior 
Washington, D.C. 20590 



13. Type of Report and Period Covered 

Final Report 
, August 1974-March 1976 



Dept. of Tri^porfetion 



I 



314. Sponsoring Agency Cod 



M-0318 



JAN y 1978 



15. Supplementary Notes 



? '"-5'-? 



16. Abstract 



Operational testing and evaluation of commercially available remote sensing 
data including space imagery, side-looking airborne radar, black-and-white, 
color infrared, color, and low sun angle photography. Multispectral scanner 
data (including thermal infrared), and airborne geophysical systems over the 
East River Mountain tunnel in West Virginia and the Carl in Canyon tunnel in 
Nevada demonstrates that, if integrated with conventionally acquired geologic 
data, remote sensing can reduce the cost of tunnel site selection and eval- 
uation and in almost every instance provides unique geologic information. 
There is no single array of remote sensors that is optimal for all tunnel 
sites, but there is a suite of remotely sensed data including space imagery, 
black-and-white and color aerial photography, low sun angle photography, and 
side-looking airborne radar (if it already exists) that should be analyzed 
for most sites because of high information content and relatively low cost. 
Several other systems including side-looking airborne radar, thermal infra- 
red scanners, and airborne geophysical systems can provide uniquely valuable 
geologic information under particular sets of geologic and climatic con- 
ditions, but are deemed too expensive for inclusion in all tunnel site 
evaluation programs. 



17. Key Words 

Remote sensing. Geology, Tunnels, 
Geologic modeling, Cost effective- 
ness. Orbital Data, Radar, Photo- 
graphy, Scanners, Airborne Geo- 
physics 



18. Distribution Statement 



No restrictions. This document is avail- 
able to the public through the National 
Technical Information Service, 
Springfield, Virginia 22161 



19. Security Classif. (of this report) 

Unclassified 



20. Security Clossif. (of this page) 

Unclassified 



21. No. of Pages 

352 



22. Price 



Form DOT F 1700.7 (8-72) 



Reproduction of completed page authorized 



INTRODUCTION 




2.1 


Purpose of 


Investigation 


2.2 


Background 




2.3 


History of 


Project 


2.4 


Objectives 




2.5 


Scope 




2.6 


Acknowledgements 


APPROACH 





TABLE OF CONTENTS 

1.0 EXECUTIVE SUMMARY 1 

2.0 INTRODUCTION 5 

5 

6 

8 

10 

n 

12 

3.0 APPROACH 13 

3.1 Underlying Assumptions 13 

3.2 Literature Search 14 

3.3 Cost Effectiveness Evaluation 16 

4.0 TECHNICAL DISCUSSION 18 

4.1 Previous Work 18 

4.2 Tunneling Conditions and Significant Geologic Features 29 

4.2.1 Significant Geologic Features 31 

4.2.2 Soil and Rock Type 31 

4.2.3 Alteration 32 

4.2.4 Geologic Structure 33 

4.2.5 Discontinuities 34 

4.2.6 Groundwater 34 

4.2.7 Ground Stresses 35 

4.2.8 Ground Temperature 36 

4.2.9 Hazardous Gases 36 

4.2.10 Earthquakes 37 

4.3 Airborne Remote Sensors Considered and Systems Selected for 

Tunnel Site Investigations 37 

4.3.1 Sensor Criteria and Airborne Sensor Selection 40 

4.3.2 Airborne Remote Sensing Systems 41 

Gamma Ray Spectrometry 41 

Ultraviolet Imagery 41 

Metric Camera 41 

Low Sun Angle Photography 42 

Multiband Cameras 43 

Multi spectral Scanners 44 

Infrared Scanners 44 

Infrared Spectroradiometry 45 

Microwave Radiometer 45 



n 



Scatterometers 46 

Imaging Radar 46 

Airborne Geophysical Surveys 48 

Airborne Electromagnetic Systems 49 

Airborne Magnetometer 50 

4.3.3 Satellite Remote Sensors 50 

4.3.4 Other Remote Sensors 51 

4.3.5 Sensor Complement Selected 51 

5.0 SITES SELECTED 52 

5.1 Carl in Canyon Tunnel Site 52 

5.1.1 Project Area Description 52 

5.1.2 Geologic Setting 52 

5.1.3 Site Geology 52 

5.1.4 Site Investigation 55 

5.1.5 Ground Conditions 56 

5.2 East River Mountain Tunnel Site 56 

5.2.1 Project Area Description 56 

5.2.2 Geologic Setting 58 

5.2.3 Site investigations 60 

5.2.4 Ground Conditions 60 

6.0 SITE INVESTIGATIONS 61 

6.1 Pre-Flight 61 

6.2 Fl ight Support 61 

6.3 Data Analysis Verification 62 

7.0 DATA ANALYSIS 66 

7.1 Satellite Imagery 66 

7.1.1 Carl in Canyon Site 67 

7.1.2 East River Mountain Site 70 

7.2 Radar Imagery 73 

7.2.1 Carl in Canyon Site 73 

7.2.2 East River Mountain Site 77 

7.3 Low Sun-Angle Photography (LSAP) 77 

7.3.1 Carl in Canyon Site 80 

7.3.2 East River Mountain Site 83 



m 



7.4 Analysis of Aerial Photography 85 

7.4.1 Carl in Canyon Site 85 

7.4.2 East River Mountain Site 96 

7.5 Multi-Band Photography 102 

7.6 Multispectral Scanner (MSS) Imagery 108 

7.6.1 Carl in Canyon Site 108 

Densitometry of Multispectral Images 109 

Additive Color Enhancement 112 

Spectral Band Ratioing 112 

Spectroradiometric Investigations 117 

7.6.2 East River Mountain Site 117 

7.7 Thermal Infrared Imagery 117 

7.7.1 Carlin Canyon Site 118 

7.7.2 East River Mountain Site 123 

7.7.3 Other Examples of Thermal Imagery 132 

7.8 Magnetometer Survey, East River Mountain 139 

7.9 Airborne Electromagnetic Surveys (AEM) East River Mountain 141 

8.0 THREE-DIMENSIONAL MODELING 143 

8.1 Carlin Canyon Model 144 

8.2 East River Mountain Three-Dimensional Model 144 

8.3 Limitations of the Three-Dimensional Model 146 

9.0 ECONOMIC ANALYSIS OF REMOTE SENSING AND CONVENTIONAL SITE 

INVESTIGATION TECHNIQUES 147 

9.1 Introduction 147 

9.2 Conventional Means of Data Collection 148 

9.2.1 Information Search 148 

9.2.2 Aerial Photograph Interpretation 151 

9.2.3 Surface Mapping 151 

9.2.4 Surface Geophysical Surveys 152 

9.2.5 Soil and Rock Borings 153 

9.2.6 Borehole Logging 155 

9.2.7 Exploratory Excavations 156 

9.2.8 Laboratory Testing 156 

9.3 Effectiveness and Cost of Remote Sensing Systems 157 



IV 



9.3.1 Satellite Data 162 

9.3.2 Side-Looking Airborne Radar (SLAR) 163 

9.3.3 Airborne Camera Systems 164 

9.3.4 Scanning Systems (Multispectral , Thermal) 165 

9.3.5 Airborne Geophysical Systems 167 

9.4 Appraisal of Combined Conventional and Remote Sensing 
Investigation Systems 167 

9.5 Cost Effectiveness of Combined Conventional and Remote 
Sensing Systems 173 

10.0 CONCLUSIONS 178 

11.0 RECOMMENDATIONS 183 

11.1 Recommended Sensor Complement 183 

11.2 Consideration of Seasonal and Diurnal Effects 185 

11.3 Recommendations for Future Work 189 

12.0 FIELD VERIFICATION PLAN 192 

12.1 Carl in Canyon Site 192 

12.1.1 Geology 192 

12.1.2 Features to be Verified 193 

12.1.3 Verification Plan 194 

12.2 East River Mountain Site 197 

12.2.1 Geology 197 

12.2.2 Features to be Verified 198 

12.2.3 Verification Plan 199 

APPENDICES 



A. REFERENCES CITED AND BIBLIOGRAPHY 

B. GLOSSARY 

C. BASIC IMAGERY INTERPRETATION 
1.0 INTRODUCTION 

2.0 PHOTOGEOLOGICAL INTERPRETATION KEYS 
3.0 LANDFORM ANALYSIS 

3.1 Sedimentary Landforms 



201 
219 
240 
240 
243 
248 
248 



3.1.1 Clay Shale 248 

3.1.2 Sandy Shale 248 

3.1.3 Sandstone 249 

3.1.4 Limestone 249 

3.1.5 Tilted Sedimentary Rocks 250 

3.2 Igneous Landforms 250 

3.2.1 Granite 250 

3.2.2 Basalts and Fast Cooled Lavas 251 

3.2.3 Tuff (Volcanic Ash Deposit) 252 

3.2.4 Interbedded Pyroclastics and Flows 252 

3.2.5 Dikes 252 

3.3 Metamorphic Landforms 253 

3.3.1 Gneiss 253 

3.3.2 Schist 253 

3.3.3 Slate 254 

3.3.4 Serpentine 254 

D. LOW SUN ANGLE PHOTOGRAPHY (LSAP) MISSION PLANNING 255 
1.0 DISCUSSION 255 
2.0 MATHEMATICAL CALCULATION OF SOLAR ELEVATION AND AZIMUTH 257 
3.0 GRAPHIC SOLUTION 260 
4.0 VISUAL OBSERVATION 262 

E. FIELD REFLECTANCE STUDIES AT CARLIN CANYON, NEVADA 263 
1.0 SPECTRORADIOMETRIC FIELD INVESTIGATIONS 263 
2.0 FIELD RADIOMETRY 265 

2.1 Exotech Radiometer Field Data (E-Channels) 265 

2.1.1 Sky Illuminance Effect 265 

2.1.2 Field Data Selection 266 

2.1.3 Field Data Reduction 266 

2.2 Exotech Results 267 
2.2.1 Summary 271 

2.3 Bar Graph 272 

2.4 Supplemental Information on Exotech Reflectance Measure- 
ments 274 

F. MULTISPECTRAL AND THERMAL INFRARED DATA ACQUISITION AND PROCESSING 

278 

vi 



1.0 DATA ACQUISITION 278 

1.1 Description of DS-1 230/1 250 Multi spectral Scanner 278 

1.2 Spectral Configurations Used 279 

1.3 Scanner Operation 280 

2.0 DATA PROCESSING 285 

2.1 Description and Operation of DS-1850 Multispectral 
Ground Station 285 

2.2 Multispectral Processing Algorithms 288 

G. AIRBORNE ELECTROMAGNETIC SYSTEM (DIGHEM) 302 

1.0 INTRODUCTION 302 

2.0 SURVEY DESCRIPTION 304 

3.0 DATA PRESENTATION 306 

3.1 The Three Conductor Models 306 

3.2 Resistivity Mapping with DIGHEM 306 

3.3 Magnetics 308 

H. COMMERCIALLY AVAILABLE RADAR AND AIRBORNE ELECTROMAGNETIC SURVEY 

SERVICES 311 

1.0 RADAR 311 

2.0 ELECTROMAGNETIC SURVEYS 313 

I. ACQUISITION OF EXISTING REMOTE SENSOR DATA FROM FEDERAL AGENCIES 315 

1.0 EROS DATA CENTER 315 

1.1 EROS Data Reference Files 315 

1.2 EROS Applications Assistance Facilities 317 

1.3 LANDSAT (Earth Resources Technology Satellite) Data 318 

1.4 Skylab Data 320 

1.5 NASA Aerial Photography 321 

1.6 Aerial Mapping Photography 322 

1.7 The Geographic Search and Inquiry System 323 

1.8 Placing An Order 324 

2.0 OTHER GOVERNMENT AGENCIES 325 

2.1 U.S. Department of Agriculture 325 

2.2 National Oceanic and Atmospheric Administration 325 

2.3 NOAA Browse File Locations 325 

2.4 National Ocean Survey 327 



vn 



LIST OF FIGURES 

Page 

Figure 1 Electromagnetic Spectrum 39 

Figure 2 Aerial Oblique View of Carl in Canyon, Nevada 53 

Figure 3 Aerial Oblique View of East River Mountain 

Virginia - West Virginia 57 

Figure 4 LANDSAT Imagery of Carl in Canyon 68 

Figure 5 Skylab Photography of Carl in Canyon 69 

Figure 6A LANDSAT Color Composite Image of East River 

Mountain Area 71 

Figure 6B LANDSAT, Band 5 (Red) Image of East River 

Mountain Area 72 

Figure 7 Skylab S-190A (Red Band) Photograph of East River 

Mountain 74 

Figure 8 Skylab S-190B Color Photograph of East River 

Mountain 75 

Figure 9 Radar Imagery of Carl in Canyon 76 

Figure lOA Radar Imagery of East River Mountain 78 

Figure lOB Radar Imagery of East River Mountain, Annotated 

With Geological Interpretation 79 

Figure 11 Morning Low Sun Angle Photography (LSAP) of 

Carl in Canyon 81 

Figure 12 Evening Low Sun Angle Photography (LSAP) of 

Carl in Canyon 82 

Figure 13 Morning Low Sun Angle Photography (LSAP) of 

East River Mountain 84 

Figure 14 Evening Low Sun Angle Photography (LSAP) of 

East River Mountain 86 

Figure 15 Low Sun Angle Photographic Enhancement of 

Sinkholes 87 

Figure 16 Annotated Black-and-White Panchromatic Photograph 

of Carl in Canyon 89 

viii 



Figure 17 Color Infrared Aerial Photograph of Carl in Canyon 90 

Figure 18 Stereotriplet of the Color Aerial Photography 

of Carl in Canyon 91 

Figure 19 Geological Map of the Carl in Canyon Nevada Area 92 

Figure 20 Ground Photograph of a Major Fault North of the 

East Portal, Carl in Canyon Tunnel 93 

Figure 21 Exposed Fault Plane Above the East Portal of the 

Carl in Canyon Tunnel 95 

Figure 22 Angular Unconformity Exposed South of the East 

Portal of the Carl in Canyon Tunnel 95 

Figure 23 Color Infrared Photography of the East River 

Mountain Area 97 

Figure 24 Outcrop of the Tuscarora Sandstone, East River 

Mountain 99 

Figure 25 Lichen Cover on the Tuscarora Sandstone 99 

Figure 26 Stereogram of Color Photography of Carl in Canyon 100 

Figure 27 Closeup View of the Diamond Peak Conglomerate 104 

Figure 28 Closeup View of the Strathearn Limestone 104 

Figure 29 Response Curves of the Filters and Films used in 

the Multiband Photography Experiment 105 

Figure 30 Multiband Photographs of the Carl in Canyon Area 106 

Figure 31 Photo "Ratioed" Image of a Scene in Carl in Canyon 107 

Figure 32 Mul tispectral Images of Carl in Canyon 110 

Figure 33 Color Composite of a Mul tispectral Image of 

Carl in Canyon 113 

Figure 34 Ratioed Image of the Mul tispectral Imagery Showing 

Enhancement of the Ferric Iron Bearing Zones 114 

Figure 35 Color Composite of Ratioed Multispectral Images 
Showing Enhancement of the Ferric Iron Bearing 
Zones 116 

Figure 36 8-lOym Thermal Infrared Image of Carl in Canyon 120 

Figure 37 Ratioed Thermal Image (8-10ym/10-12ym) of the 

Carl in Canyon 1.21 



IX 



Figure 38 Daytime Thermal Infrared (10-12ym) Image of the 

East River Mountain 124 

Figure 39 "Contour" Display of Daytime Thermal Infrared 

Imagery (8-lOym) of the East River Mountain 125 

Figure 40A Nighttime 8-1 Oym Thermal Imagery of the East 

River Mountain 127 

Figure 40B Nighttime 10-12ym Imagery of the East River 

Mountain 128 

Figure 41 Ratioed Image of Figures 40A and 40B (8-lOym/ 

10-12ym) 130 

Figure 42 Closeup View of the Rose Hill Formation 131 

Figure 43 Thermal Imagery (8-1 4ym) Showing Enhancement of 

Structure and Stratigraphy 134 

Figure 44 Aerial Photograph of Areas Shown in Figure 43 135 

Figure 45 Comparison of Aerial Photography and Thermal 

Infrared Imagery 136 

Figure 46 Small Scale Thermal Infrared Imagery 137 

Figure 47 Thermal Infrared Imagery for Landslide Mapping 138 

Figure 48 Interpretation Map of Airborne Geophysical Data 140 

Figure 49 A-D Basic Drainage Patterns 244 

Figure 49 E-H Basic Drainage Patterns 246 

Figure 50 Illustration of Low-Sun-Angle Shadow Enhancement 256 

Figure 51 Diagrammatic Explanation of Hour Angle 258 

Figure 52 Smithsonian Chart for Solar Altitude and Azimuth 

Determination 260 

Figure 53 Relative Reflectance Measurements Made at Carl in 

Canyon 264 

Figure 54 Graph of Spread of Ratio Means for R-54 and R-75 273 

Figure 55 Exotech Radiometers in Calibration Mode 275 

Figure 56 Radiometer Orientation for Hemispherical Reflec- 
tance Measurements 277 



Figure 57 Radiometric Orientation for Bi-Directional Reflec- 
tance Measurements 277 

Figure 58 Scanner Configuration for Day Flights 281 

Figure 59 Scanner Configuration for Night Flights 282 

Figure 60 Relative Spectral Response of the Detector/Filter 

Combinations 283 

Figure 61 Ground Station for Processing Tape Recorded Multi- 

spectral Data 286 

Figure 62 Flow Diagram of Image Processing Steps 287 

Figure 63 Multicoil Configuration of DIGHEM Bird 302 

Figure 64 Dighem System Conducting a Survey 303 

Figure 65 Electromagnetic Survey Flight Record 307 

Figure 66 Conductive Earth Model: Two-Layer Case 309 

Figure 67 Example of an Apparent Resistivity Map 310 



XT 



LIST OF PLATES (In Pocket) 

Plate I Three-Dimensional Geologic Model of the Carl in Canyon, 
Nevada Tunnel Site 

Plate II Three-Dimensional Geologic Model of the East River 
Mountain, Virginia - West Virginia Tunnel Site 

Plate III Aeromagnetic Survey, East River Mountain Site 

Plate IV Airborne Resistivity Survey, East River Mountain Site 

Plate V Remote Sensor Survey, Integrated Interpretation, East 
River Mountain Site 



xn 



LIST OF TABLES 



Page 



Table 1 Summary of Pertinent Data for Imagery: East 

River Mountain 63 

Table 2 Summary of Pertinent Data for Imagery: Carl in 

Canyon 64 

Table 3 Multispectral Cahnnels and Bandwidths 109 

Table 4 Densitometric Measurements of Multispectral 

Prints 111 

Table 5 Comparison of Formation Thicknesses at East River 

Mountain 145 

Table 6 Conventional Investigation Techniques for Tunneling 149 

Table 7 Factors Controlling Cost of Remote Sensing Data 

Acquisition 158 

Table 8 Remote Sensing Site Investigation Techniques for 

Tunneling 159 

Table 9 Capability Ratings of Conventional and Remote 

Sensing Methods Under Optimum Conditions 171 

Table 10 Comparison of Investigation and Construction 

Costs 176 

Table 11 Ground Geophysical Methods for Surveying Tunnel 

Sites " 195 

Table 12 Ephemeris of the Sun 259 

Table 13 Field Measured Radiometric Data 268 

Table 14 Field Measured Radiometric Data Ratios 269 

Table 15 Summary of Reflectance Group Average Values of 

Means 270 

Table 16 Multispectral and Thermal DAta Processing: 

Carl in Canyon 290 

Table 17 Multispectral and Thermal Data Processing: 

East River Mountain 297 



xm 



Table 18 Mul tispectral and Thermal Data Processing: 

Big Walker Mountain 301 

Table 19 Chart of Abailable Electromagnetic Systems 

and Operating Parameters 314 



XIV 



EVALUATION OF AERIAL REMOTE SENSING TECHNIQUES FOR DEFINING 
CRITICAL GEOLOGIC FEATURES PERTINENT TO TUNNEL 
LOCATION AND DESIGN 



1.0 EXECUTIVE SUMMARY 

The cost of tunnel construction often far exceeds original esti- 
mates due to unforeseen geological conditions that create work delays 
and require more costly excavation and construction procedures. The 
degree to which the rock structure and engineering properties of the 
different rock materials can be predicted at tunnel depth depends upon 
a number of factors such as rock type, structural complexity, climate, 
and degree of surface exposure. This latter factor is extremely impor- 
tant because to a large extent the prediction of geological conditions 
at tunnel depth is based on the mapping of the surface geology. A 
certain number of core drill tests, some geophysical surveys, and in 
some instances test excavation, supplement surface mapping. 

Developments in airborne remote sensing instrumentation over the 
last decade or two have created a new suite of sensing systems and 
improvements to existing systems. These systems show promise of ac- 
quiring better and more comprehensive geological information for a 
tunnel site or acquiring this information more quickly or cheaply than 
the conventional investigative procedures now used. 

The objective of this investigation was to conduct actual field 
tests using various airborne remote sensing techniques for the purpose 
of evaluating their contribution to the investigation and selection of 
tunnel sites by the development of improved three-dimensional geological 
models. 

Two tunnels in substantially different environments were selected 
for investigation. The Carl in Canyon site near Elko, Nevada, receives 
approximately four inches (10cm) of rainfall annually. The East River 
Mountain tunnel located in southeastern West Virginia, receives an 
annual rainfall of 40-60 inches (100-1 50cm). 

To be of greatest value any airborne remote sensing technique must 
be thoroughly integrated with conventional tunnel site investigation and 
evaluation programs. There is no single array of remote sensors that 
will be optimal for all tunnel sites. However, there is a suite of 
remotely sensed data that we believe should be acquired and analyzed for 
most tunnel sites because of its relatively low cost and high infor- 
mation content. This data package includes LANDSAT and Skylab satellite 
imagery, black-and-white and color aerial photographs, low sun angle 
photography, and side-looking airborne radar (SLAR) if it exists. 
Analysis of these data and existing geologic information will provide a 
basis for planning additional remote sensing surveys and the conven- 
tional geologic evaluation program. A decision to use other airborne 
remote sensing systems must be guided by the geology and climate of the 

1 



area, the amount of detailed geologic data that cil ready exists, and time 
and budgetary limits of the program. 

There are several remote sensor systems that may provide valuable 
information under a particular set of geologic or climatic conditions, 
but that are deemed to be too expensive for inclusion in all tunnel site 
evaluation programs. Sensors in this category are SLAR (if it must be 
contracted for a specific site), airborne geophysical systems, and 
multispectral and thermal scanner systems. Because of its high cost, 
SLAR should be contracted for a specific site only if the site is in an 
area where cloud cover has precluded the acquisition of satellite ima- 
gery and photography. If the site is in a geologically complex area 
where the complexities are likely to be reflected by conductive or 
magnetic zones, airborne geophysical systems (magnetic and electromag- 
netic) will provide invaluable information which can help in predicting 
geologic conditions at tunnel level. Airborne magnetometer and electro- 
magnetic systems were used over the East River Mountain site. Thermal 
infrared scanner imagery will provide unique geologic information in 
areas where soil moisture difference may reflect geological structure, 
where there is little surface vegetation, or where differences in rock 
type are marked by differences in silica content or thermal inertia 
properties. 

The results in this investigation demonstrated, as anticipated, 
that the color and black-and-white aerial photography were the prime 
sources of information. However, each sensor provided some unique 
information. Satellite imagery gave a synoptic overview of an area and 
a regional view of the geological structure. This imagery revealed long 
subtle, linear features, that in many instances proved to be large 
fracture or fault zones not identifiable on larger scale imagery. 
Several features of this type are present in the vicinity of the project 
tunnel sites, particularly the Nevada site. 

Radar imagery confirmed some of the previously detected linear 
features and added detail to the understanding of the regional geology 
surrounding the tunnel sites. The imagery showed that the Nevada site 
is structurally complex and that major faults are present in the vicin- 
ity of the tunnel . 

Color infrared photography was of little value at either site. The 
principal value of this photography lies in the emphasis it gives vege- 
tational patterns. The Carl in Canyon site was overflown in late October 
and the East River Mountain site in early April, when the vegetation was 
dormant in both areas. 

Low-sun-angle photography emphasizes the control that geologic 
structure exerts on the development of the landforms in each area. This 
imagery revealed numerous linear features, some of which were faults 
identified using data from other sensors. Multispectral and thermal 
infrared imagery was acquired at both test sites. The analyses of these 
various data were conducted using both conventional photographic and 

2 



computer image enhancement techniques. The tape recorded scanner data 
was processed with a variety of algorithms by a special purpose com- 
puter. These algorithms included density slicing, density stretching, 
contour enhancement, and channel ratioing. Images from this processing 
were further analyzed with the aid of additive color devices and photo- 
graphic laboratory color processing. 

Visible and near-visible multispectral scanner data of the eastern 
site proved of little value because of the limited number of outcrops 
and the masking of most rock surfaces by lichens. At the western site, 
where the lichen cover is more sparse, ratioing of selected spectral 
bands emphasized the presence of iron and specific stratigraphic hori- 
zons. 

In the Carl in Canyon area, analysis of each of the two spectral 
bands (8-lOym and 10-12ym) of the thermal imagery provides little infor- 
mation except for soil -outcrop boundaries. Structural features that 
coincide with these boundaries are emphasized. However, ratioing of the 
two thermal bands accentuated several outcrops of materials high in 
silicate content because of the emission minima of silica in the 8-lOym 
region of the spectrum. 

Because of the heavy lichen cover on most outcrops at the East 
River Mountain site, ratioing of the thermal imagery emphasized silica 
rich formations only in areas recently disturbed by man's activities. 
The two thermal bands used have nearly the same sensitivity to moisture 
differences, thus imagery from both bands revealed a significant number 
of geologic features enhanced by differences in the distribution of soil 
moisture. 

The aeromagnetic data showed several weak anomalies that correlated 
well with two linear features identifiable on the photography, which 
supports the hypothesis that these features are faults. The strongest 
magnetic anomalies were associated with the steel within the tunnels. 

The electromagnetic data identified two anomalous areas. One area, 
near the north portal of the East River Mountain tunnel is interpreted 
as an interconnecting, canvern-sinkhole zone, saturated with water. The 
second area, on the south slope of the mountain, is a circular anomaly 
interpreted as a water saturated intersection of two fault zones. Other 
remote sensing data support this interpretation. 

There is no single optimum time of day or season of year for all 
sensors. A near-optimum time period for flying an individual sensor can 
be selected with little difficulty, but multiple sensor missions must be 
planned with consideration of a number of environmental factors pre- 
vailing at the site. 

The cost of conventional procedures for geologic evaluation of a 
specific tunnel site are not difficult to derive. The same is true for 
the acquisition and analysis of any of the remote sensor data. However, 



for a specific site prior to tunnel construction, it is extremely diffi- 
cult to assess the cost effectiveness of using a suite of remote sensors. 
If no difficulty in excavation of a tunnel is encountered after the 
expenditure of a sum of money for the acquisition and analysis of remote 
sensing data, the benefits will be minimal and equal only to the cost 
savings of using an integrated conventional and remote sensing approach 
over a completely conventional approach. However, if major problems are 
detected and avoided because remote sensing was included, the benefits 
may be large. We believe that the remote sensing systems tested do have 
the capability of detecting problems that conventional approaches alone 
might miss. 



2.0 INTRODUCTION 

2.1 Purpose of Investigation 

A critical element in the safe and successful completion of a 
tunnel is the accurate prediction of the geological and engineering 
characteristics of the rock mass to be encountered. These pre- 
dictions depend on the quality and quantity of the geological, 
geophysical, and engineering data collected and the proper inter- 
pretation and analysis of these data prior to the start of excavation. 

The geologic data essential to tunnel planning and construction 
are those which define the ground conditions surrounding the pro- 
posed tunnel in terms which can be directly related to the equipment, 
construction materials, labor, and tunneling techniques required 
for safe and economical construction. In other words, the geologic 
data must relate to the engineering parameters required for design 
and construction. This generally implies a three-dimensional 
understanding of the distribution of pertinent geological features 
surrounding the proposed tunnel and extending radially from the 
center line of the tunnel bore far enough to include the total 
influence on the tunnel construction. 

Geologic principles are sufficiently understood that a know- 
ledge of geologic conditions in one area will permit the extrapo- 
lation of the known geology to an adjacent area. In other words, 
the visible is an inexpensive guide to the invisible. The degree 
of success to which this can be accomplished is dependent upon the 
amount of information available and the complexity of the area. 
For this reason tunnel geologists carefully examine the surface 
geology prior to embarking on any program of subsurface exploration. 
It is also for this reason that a variety of techniques generally 
described as remote sensing offer a distinct promise of assisting 
the initial surface geologic exploration. 

The acquisition of data for planning purposes largely consists 
of field mapping of the geology, supplemented as necessary by 
accoustical and resistivity surveys, drilling programs, and aerial 
photographic mapping. The latter technique is classified along 
with other imaging and non-imaging mapping techniques as remote 
sensing. This term is applied herein to the use of any system used 
to acquire data about an object or area from a remote point. It 
has been applied somewhat loosely to a series of sensor systems, 
normally airborne, which detect reflected and emitted electro- 
magnetic energy in the ultra violet, visible, and longer wavelength 
portions of the spectrum. It also includes force field detectors 
such as the magnetometer and the gravimeter. 

The purpose of this study is to evaluate, in terms of cost and 
quality of data, the capability of airborne remote sensing techniques 
to provide geologic data for tunnel site selection and evaluation. 



VJe wanted to make the assessment as realistic as possible (only 
commercially available systems are considered) and the results 
immediately useful to the industry (methods results and special 
considerations are thoroughly discussed). 

Aerial remote sensing techniques can provide significant in- 
formation needed by engineers and geologists for tunnel planning and 
design. Remote sensing is not, however, a panacea that will replace 
conventional geologic and engineering techniques. In fact, the 
maximum benefit is derived from this new technology when it is used 
in conjunction with conventional techniques. Remote sensing tech- 
niques can be used to acquire information more rapidly than is 
possible by conventional ground methods, and in many instances 
provides information not previously available. 

For those types of data that cannot be collected from the air, 
remote sensing can be used to plan efficient ground surveys and can 
be used to rapidly extend the results of such surveys to larger 
areas. For example, while remotely sensed data can not eliminate 
the need for test boring, it may be used to guide a drilling program 
so as to optimize the information obtained from each hole (perhaps 
reducing the number of holes necessary) and providing a means of 
projecting this information from each hole over a larger area. 
Experience has demonstrated that many of the largest geologic 
features go unobserved during ground investigation. One of the 
major contributions of remote sensing to tunnel construction can be 
the recognition and assessment early in the planning stages of a 
tunnel project of geologic features such as major shear zones, 
serpentine bodies, and etc., which may pose a hazard. 

2.2 Background 

Both the engineering profession and the public generally 
regard tunneling as an operation involving an unusual degree of 
risk. The nature of this risk, however, is not well understood 
outside the tunneling industry. There is the risk of encountering 
subsurface conditions that prevent completion of the project. There 
are a few subsurface conditions such as wery high temperatures and 
yery high and continuous groundwater inflows which may permanently 
stop the advance of a tunnel, but modern tunneling technology pro- 
vides the tools for coping with almost any ground condition en- 
countered at the depth of interest in tunneling. The risk of the 
technical impossibility of tunneling is therefore small. 

Second, is the risk of encountering subsurface conditions that 
will either slow or temporarily stop tunneling progress. There are 
many examples of this type of subsurface conditions including 
fallouts, flowing ground, groundwater inflows, weak zones, hard 
zones etc. In some instances the method of excavation or support 
system is modified while in other instances the method of tunneling 



is completely changed to cope with these conditions. In either 
situation, the cost of performing the work is increased and com- 
pletion of the work is often delayed. 

Third, there is a risk of encountering a subsurface condition 
which will affect the safety of the workmen in the tunnel or the 
safety of surface or near surface structures or the safety of the 
public. Flooding of the tunnel, high temperatures, and toxic gases 
are examples of conditions which affect the safety of the workmen. 

The degree of risk from tunnel to tunnel is not uniform, but 
varies with the geologic conditions, the characteristics of the 
tunnel and the method of construction. Risk is primarily the 
result of uncertainty of the geologic conditions to be encountered 
by the tunnel and could be largely eliminated if tunnel site in- 
vestigations provided a complete and accurate picture of the sub- 
surface conditions prior to tunnel excavation. With a perfect 
picture of the geologic conditions, the ground behavior during 
excavation could be predicted accurately and the tunnel design and 
method of construction could be adapted to the existing conditions. 
In this ideal situation, construction schedules and tunnel cost 
estimates would be more accurate and tunneling costs would decrease. 

On some tunneling projects, the preconstruction model of 
geologic conditions approaches the ideal proposed above because of 
excellent exposures of the material present at tunnel level or an 
unusually intensive investigation program. However, a comparison 
of preconstruction and construction geologic records normally 
reveals that the preconstruction model of geologic conditions was 
incomplete and lacked information about geologic features which 
significantly affected construction. The preconstruction model of 
geologic conditions may be deficient because of inadequate inves- 
tigation or an incomplete evaluation of available information, but 
most frequently the deficiencies of the model are the result of the 
limitations of conventional investigation methods. 

Conventional investigations include two or more of the follow- 
ing methods: 

review of previous geologic studies 

review of previous construction records 

interpretation of aerial photographs 

geologic mapping 

geophysical testing 

borings 

borehole logging and testing 

exploratory excavations 

field testing 

laboratory testing 



In most instances, the geologic conditions at tunnel level are 
predicted from an incomplete record of surface and near-surface 
geologic features and from a relatively restricted set of sub- 
surface data. Predictions generated from this information are good 
when the available information is representative of the bulk of the 
rock and at the same time identifies most of the anomalies or 
discontinuities. 

Any means of investigation that could cost effectively improve 
the completness of the surface or subsurface record would naturally 
be of value to the tunnel industry. Recent work indicates that 
airborne remote sensing methods can assist tunnel site selection 
and investigations by providing: 

A. Reconnaissance studies for highway and tunnel routing. 

B. Selection of a specific tunnel site along a given route. 

C. Location of features to be checked by geologic mapping. 

D. Identification of geologic trends which are only partially 
exposed and not completely identified during geologic 
mapping. 

E. Identification of geologic features which are concealed 
by soil and would be completely missed in conventional 
geologic field mapping. 

2.3 History of Project 

Work commenced on the project on 23 August 1974 upon notifi- 
cation by the U.S. Department of Transportation (DOT) to proceed. 

The Request for Proposal listed four tunnel sites for consid- 
eration, two in the western and two in the eastern United States. 
One site was to be selected in each geographic area. The sites 
considered were: 

• Big Walker P^ountain Tunnel in Virginia; 

• East River Mountain Tunnel on the Virginia-West Virginia 
border; 

• Straight Creek Tunnel in Colorado; 

• Carl in Canyon Tunnel in Nevada. 

Straight Creek and East River Mountain seemed to offer the greatest 
variety of geologic and climatic conditions for testing various 
sensor systems. The initial assessment of the sites indicated that 



the probable optimum seasons for remote sensor data collection were 
summer or early fall for the western sites and early spring for the 
eastern sites. 

To complete the study in 18 months, it was deemed necessary to 
acquire data on the western site in the fall of 1974. 

As it was not possible to conduct the preliminary site in- 
vestigations and mobilize the survey equipment before 1 October, the 
Straight Creek Site in Colorado, the only tunnel in igneous and 
metamophic rocks, was not considered. Elevations there exceed 
12,000 feet and snow cover was anticipated on the site before 
October. Other considerations by the Federal Highway Administration 
(FHWA) also negated the use of this site; consequently, the Carlin 
Canyon site near Elko, Nevada was selected. 

Mobilization to Elko was set for 17 October. The aerial 
surveys were made on 18, 19, and 20 October. The color and color- 
infrared and low-sun-angle infrared photography was flown by Olympus 
Aerial Surveys, Inc. , on the 18th. The scanner aircraft, supplied 
by Aerial Surveys, Inc., made the night time thermal infrared survey 
overflight between 11 and 12 p.m. on the 18th. Daytime thermal 
imagery and multi spectral imagery were flown on the 19th. Because 
there was a question about quality of the thermal data recorded 
during the night flight, this survey was rescheduled as a predawn 
flight on the 20th and completed just before sunrise at aircraft 
altitude. 

The two eastern tunnel sites, Big Walker Mountain in Virginia 
and East River Mountain on the Virginia-West Virginia border, are 
only 20 miles apart and cut nearly identical stratigraphic sections. 
The East River Mountain site had been tentatively selected primarily 
because it appeared to have better rock exposures. Field investi- 
gations in the spring of 1975 confirmed that the East River Mountain 
tunnel site was the the better of the two sites for the study. 

The time window for the survey of the eastern site was rela- 
tively narrow and had to be made between the time of complete snow 
melt and development of a leaf canopy; the latter would occur in 
late April or early May. The photographic and scanner surveys were 
scheduled for the first week of April. 

Mobilization by Daedalus Enterprises commenced on 31 March 
1975. The survey aircraft flew to Bluefield, West Virginia, on 
1 April, arriving about 12:30 p.m., and the multispectral survey of 
the site was made before landing. The equipment was modified for 
thermal mapping and daytime thermal imagery was flown about 4:30 
p.m. The nighttime thermal survey was made about 11 p.m. to avoid 
ground fog conditions which developed in that area in the early 
morning hours. 



Low sun angle photography was flown on 5 and 7 April. Color 
and color- infrared photography was acquired on the 6th, but had to 
be reflown. Cloud cover and wind delayed these reflights until 27 
April. 

The results of the multispectral data analyses indicated that 
it was desirable to acquire spectroradiometric data on the different 
rock types at Carlin Canyon. Although such detail was beyond the 
scope of work, the extra effort would enhance the results of the 
study. A trip to the Carlin Canyon site was made on 4-6 August 
1975. An Isco Spectroradiometer was used to measure the reflectance 
properties of the conglomerate and limestone strata. 

On 19 and 20 August a field check was made at the East River 
Mountain site to verify imagery analysis and acquire field data. 

Dr. R.J. P. Lyon of Stanford University spent the week of 
7 September at the EarthSat facility in Washington analyzing the 
multispectral data. During this same period Daedalus Enterprises 
used the services of Dr. Robert Vincent of Geospectra Corporation 
to independently evaluate thermal and multispectral imagery of the 
Carlin Canyon site. These analysis required additional field 
effort in Nevada to confirm the results and acquire additional 
radiometric information. Dr. Lyon, 0. Russell, and D. Stanczuk 
visited the site during the week of 21 October and confirmed many 
of Vincent's findings and acquired additional spectroradiometric 
measurements with two Exotech "ERTS-band" radiometers. 

Dighem Limited of Toronto Canada was contracted to make air- 
borne conductivity and magnetometer surveys over the East River 
Mountain area, and, if practical, over the Big Walker Mountain 
tunnel site. The helicopter and ground crew arrived at Bluefield, 
West Virginia on 8 October and the Virginia and West Virginia State 
Highway Departments were contacted and advised of the survey activ- 
ity. Wind seriously hampered the investigation and the crew re- 
mained on the site nearly two weeks. 

A draft of the final report was submitted to the U.S. Depart- 
ment of Transportation of 1 March 1976. 

2.4 Objectives 

Numerous advances in the development of remote sensing data 
collection and analysis have occurred in the last two decades. 
However, there are yery few studies of the potential of remote 
sensing to aid in tunnel siting investigations. Willow Run Labo- 
ratories conducted the only study of significance in 1971 and 1972 
under the auspices of the Advanced Research Project Agency (ARPA). 
The report of this investigation contains an evaluation of the 
state-of-the-art of remote sensing and an empirical assessment of 
its application to tunnel site selection. 

10 



The main objective of this study is to critically evaluate, 
through actual application, the role of airborne remote sensing in 
the selection and geological evaluation of tunnel sites. This 
involves not only determining what types of geologic data airborne 
remote sensors can provide, but what techniques are best for extract- 
ing, recording, and evaluating these data; it further involves an 
assessment of acquisition and analysis requirements in terms of 
money, time, and manpower. The specific objectives are: 

• Determine the extent to which aerial remote sensing and 
geophysical systems can be utilized to develop a three- 
dimensional geologic model to aid in tunnel location and 
design. 

• Determine the optimum combination of aerial remote sensors 
for identifying various geologic features and how these 
data can improve the accuracy of the three-dimensional 
model or reduce the time or cost necessary to obtain such 
a model. 



• 



Utilize applicable computer techniques for extracting, 
enhancing, and classifying pertinent geologic features. 

• Develop realistic economic information on cost effective- 
ness of the application of airborne remote sensing tech- 
niques to tunnel design and construction. 

2.5 Scope 

Considering the possible range of topics implied in the com- 
ponents, remote sensing and tunnel engineering, this study has a 
relatively narrow focus. The major consideration of this project 
is where do these two components overlap, and specifically what is 
the potential synergistic effect of this overlap. 

The study does not discuss the theories of electromagnetic 
radiation, the characteristic emission spectra of rocks and vege- 
tation as defined by previous investigators, or the theory of 
operation of the various sensor systems. 

The evaluation of remote sensing techniques includes some of 
the latest developments, but is restricted to those systems which 
are now commercially available. The advantages of this approach 
are that significant results can be applied immediately by the 
tunneling industry and the cost effectiveness analysis will place 
this contribution to tunneling technology in proper prospective 
with current economic conditions. Only commercially available 
computer processing and photographic services were used for the 
same reasons. New remote sensing systems, new computer software, 
or unusual photo interpretation techniques were not developed or 
considered. 

11 



A unique aspect of this study is the application of a wide 
complement of existing remote sensing systems and established 
analysis techniques to tunnel site investigations. From the en- 
gineering point of view the study does not consider the fine points 
of tunnel engineering and construction, but confines itself to a 
discussion of the geologic information, obtained by airborne remote 
sensing techniques, and as this information applies, tunnel site 
evaluation and selection. 

The study analyzes the capabilities of a suite of commercially 
available satellite and airborne remote sensing systems to provide 
data applicable to tunnel engineering and design at two specific 
test sites and extrapolates these observations to a variety of 
possible situations. 

2-6 Acknowledgments 

Numerous people have made suggestions and provided information 
and encouragement that have materially improved this report. 
Acknowledgement is given to Dr. Richard Coon of A. A. Mathews, Inc. 
who made numerous valuable contributions to this investigation in 
the form of advice on geologic engineering principles as related to 
tunnel site investigations. Dr. Coon was an important contributor 
to sections, 4.0, 5.0, and 9.0 of this report. 

Thanks are given to Dr. R.J. P. Lyon of Stanford University for 
technical advice on dichroic mirror parameters, which, unfortunately, 
due to time constraints, it was not possible to utilize to full 
advantage. His assistance in spectral radiometric field investi- 
gations and analysis of the multispectral imagery is greatly appre- 
ciated. He is the principal author of Appendix E. 

The contribution of Dr. Robert K. Vincent of Geospectra, Inc., 

in the ratioing and analysis of multispectral and thermal imagery 

is appreciated. Mr. Tom Ory of Daedalus Enterprises Inc., also 

made valuable suggestions in the imagery processing and analysis. 
He contributed Appendix F. 

The suggestions and recommendation and constructive guidance 
of Mr. Frank Perchalski, Contract Manager, Federal Highway Adminis- 
tration, are acknowledged with appreciation. 



12 



3.0 APPROACH 

The evaluation of airborne remote sensing systems for providing 
geologic information for tunnel site selection and evaluation involved 
acquiring a variety of remote sensing data over two tunnel sites. One 
test site, the East River Mountain Tunnel, is located in Virginia and 
West Virginia, and the other site, Carlin Canyon Tunnel, is located in 
Nevada. With the exception of the airborne geophysical instrumentation, 
the same suite of sensors was used at both sites in order to test the 
relative effectiveness of these systems in two distinct geologic and 
climatic environments. At each site all the sensors used were flown 
at near the same time to permit a basis of comparison among sensors 
that provide similar data. 

Data acquisition involved only commercially available remote 
sensing systems under operational conditions to insure that the 
results are immediately useful to the tunneling industry. This also 
provided a realistic basis for assessing the costs of using these 
systems. 

Comparison of the costs of acquiring geologic data by airborne 
methods, and the type, importance, and level of detail to the costs 
and quality of data that conventional means provide, formed the basis 
for assessing cost effectiveness. 

3.1 Underlying Assumptions 

In order to evaluate as objectively and realistically as 
possible the contribution of each remote sensor system used, we 
imposed several restrictions on the study by making several 
assumptions. 

The geologic analysis of each tunnel site was to be performed 
without knowledge of the geologic conditions discovered during 
construction of each tunnel. Therefore, the first assumption is 
that only preconstruction data related to lithology, structure, 
and ground conditions were to be used. 

Second, we assumed that the route and site selection process 
had been completed and that data was being collected to evaluate 
geologic conditions and anticipate hazards of construction includ- 
ing the competence of the rock, slope stability at portal areas, 
roof collapse potential (which is related to frequency of frac- 
tures), and "wet zones" due to ground water flow. 

Further, we assumed that route and site selection and site 
specific investigations will in the future be performed for 
tunnels using a multistage approach which combines conventional 
as well as remote sensing systems. Our analysis therefore did 
consider synergistic effects of using remote sensing and conven- 
tional systems. 

13 



The report is written for the tunnel geologist or engineer 
who is unfamiliar with remote sensing and how it can assist him. 

Since the interests of the readers may be varied, major 
sections of the report have been written to stand alone. For 
emphasis and for the benefit of an audience of diverse interests, 
many concepts are reiterated in varying detail throughout the 
report. 

The analyses of the various data types are presented in a 
logical sequence beginning with small scale, synoptic view, 
satellite imagery to the large scale, detailed view, aerial 
photography. The significant features are annotated on each 
image and discussed in the text. Judgments made are based on the 
analysis of the particular image and other images already analyzed. 
These judgments are modified where necessary as new information 
is derived from the analysis of additional imagery. The more 
technical aspects of the study are contained in the Appendices. 

3.2 Literature Search 

The primary value of a literature survey is that the knowledge 
gained can be used as a foundation from which advances in the art 
can be made. The literature review was conducted to define the 
state-of-the-art in applying remote sensing techniques to geologi- 
cal analysis of tunnel sites during pre-construction phases. 
Literature pertaining to all aspects of tunneling is quite exten- 
sive and to a slightly lesser degree the same is true for litera- 
ture dealing with remote sensing. There is, however, a lack of 
information available on the application of remote sensing tech- 
niques to tunneling. This fact, and the intuitive judgment of 
the potential value of remote sensing applied to tunnel site 
studies, are the prime justifications for this research and 
development project. 

In this literature search bibliographies containing over 
1,700 abstracts of publications v/ere assembled. They relate to 
tunnel engineering, remote sensing, geology, rock mechanics, and 
tunneling costs. The main sources of information included four 
computer bibliographic data searches, an annotated bibliography 
on tunneling prepared by the Department of flousing and Urban 
Development, conference proceedings, and publications from the 
files of the contractor, subcontractors, and consultants. 

The specific purpose of the literature review was to identify 
and describe systems and techniques that can be used to select a 
suitable tunnel location and design. The first objective of the 
literature was to examine the theories of operation and reported 
capabilities of a variety of aerial remote sensing instruments. 
The second objective was to identify site selection and precon- 
struction engineering problems that could be addressed using 

14 



aerial remote sensing techniques. The third objective was to 
study the previous applications of remote sensing techniques to 
tunneling. 

To initiate the search, two standard references of the 
American Society for Information Science were used: 

• A Survey of Commercially Available Computer Readable 
Bibliographic Data Bases, 

• Library and Reference Facilities in the Area of the 
District of Columbia, Ninth Edition. 

From the survey of computer readable data bases, seven 
organizations were contacted. These organizations were: 



National Technical Information 

Service 
5285 Port Royal Road 
Springfield, Virginia 22151 

Defense Document Center 
Cameron Station 
Alexandria, Virginia 22314 

Transportation Research Board 
2101 Constitution Avenue 
Washington, D.C. 20418 

Rock Mechanics Information 

Service 
Imperial College of Science & 

Technology 
Royal School of Mines 
London, England SW7 

Engineering Index, Inc. 
345 East 47th Street 
New York, New York 10017 

MARC Distribution Service, 

Card Division 
Library of Congress 
Building 159 
Washington, D.C. 20541 

Congressional Research Service 
Library of Congress 
Washington, D.C. 20540 



One search performed. 



Two searches performed, 



One search performed, 



One search performed, 



Do not perform 
searches. 



Do not perform 
searches. 



Do not perform 
searches. 



15 



Once it was determined that certain key words related to 
remote sensing and tunneling did appear in the vocabulary of four 
of the seven retrieval systems, bibliographic searches were 
requested. The searches contain several hundred articles related 
to the key vyords submitted; however, not all were relevant to the 
study. It vjas therefore necessary to review the abstracts that 
appeared in the search and select pertinent documents. All 
pertinent documents were than acquired in either microfiche or 
paper copy form, and the bibliographies of these documents were 
checked in turn for pertinent references. 

The bibliography, titled, "Tunneling: An Annotated Bibliog- 
raphy with Permuted-Title and Key-Word Index" was compiled by the 
Oakridge National Laboratory for the Department of Housing and 
Urban Development. This bibliography was obtained, but, although 
it contained approximately 1,200 articles, most of the emphasis 
was placed on small diameter tunnels in urban areas. With the 
exception of two publications, there was almost no mention of 
remote sensing applications to tunneling. A second major source 
of reference material was obtained from the standing files of the 
contractor, subcontractors, and consultants. Several papers were 
found in the Proceedings of the 1972 North American Rapid Excavation 
and Tunneling Conference. All of the documents obtained were 
reviewed according to subject, but formal review summaries were 
not prepared. The titles and authors of these documents appear in 
Appendix A. 

3.3 Cost Effectiveness Evaluation 

In approaching the question of cost effectiveness, it is not 
meaningful to state one cost savings figure and label it "cost 
savings to tunnel site investigations using remote sensing tech- 
niques," because each tunnel site is unique. The geologic, 
environment, and engineering considerations at a particular 
tunnel site determine the investigation procedures. What is more 
meaningful is to identify unit costs of investigation techniques 
and unit costs of construction. The question in this context is 
similar to the question of should one buy insurance. You may 
never need it, but if you pay a small premium to get the best 
coverage it may be possible to avoid financial disaster. In 
tunneling, the purchase of an additional unit of site investigation 
may not be needed, but if a feature that could slow or stop the 
construction is found by further investigation, then the cost is 
more than justified. 

We made several assumptions in evaluating the cost effec- 
tiveness of applying remote sensing techniques to tunnel con- 
struction: 

• The information obtained from remote sensing systems 
will supplement, not replace, information obtained by 

16 



conventional ground methods. 

• As the first stage in a multistage investigation, 
remote sensing will optimize conventional field inves- 
tigation by identifying geologic and hydrologic anomalies 
and directing second stage field investigations. The 
expenditure for field investigations may be reduced. 

• The additional unique information provided by remote 
sensing will improve the three-dimensional geologic 
model for the proposed tunnel. A model is critical in 
estimating tunnel support requirements, selecting the 
method of driving the tunnel, estimating the time re- 
quired to complete the tunnel, allocating resources, 
and planning safety procedures. 

Section 9,2 and 9.3 contain a discussion of the capabilities 
and an approximate range of costs of conventional methods of 
field investigation systems. However, costs are site specific 
and can vary greatly depending on such factors as geologic con- 
ditions, site accessibility, local topographic relief, and climate. 
The effectiveness of a system is based in part on a need for 
information and the capability of the system to fulfill that 
need. 



17 



4.0 TECHNICAL DISCUSSION 

This section summarizes previous work in remote sensing related 
to tunneling, geology, and hydrology. It describes tunneling conditions 
in terms of significant geological features and it summarizes the 
design capability of various remote sensing systems and the criteria 
used for selecting these systems for this investigation. 



4.1 Previous Work 

Whenever a new technology emerges, or an existing technology 
is applied to a new area, or an old one is reborn, there is 
almost invariably a flurry of experiments and investigations that 
are similar to previous work. The reason for this is that most 
investigations begin from common ground; that is, they are founded 
on established theories and proceed toward unknown or unproven 
hypotheses. Almost any literature survey supports this observation. 

Parker (1968) has made the prediction that "aerial reconnais- 
sance someday will supplant soil augers, rock drills, surface 
reconnaissance, and geophysical surveys as the engineer's prime 
means of obtaining information about soils and rocks." Although 
there have been significant advances in the state-of-the-art, 
aerial reconnaissance techniques can't yet replace conventional 
techniques. Furthermore, it is unlikely that this will occur in 
the near future. Mr. Parker notes "that the future application 
of remote sensing to engineering problems is more dependent upon 
improvements in image analysis rather than improvements in remote 
sensing equipment." This is a significant point, because even 
though experts in data analysis and photointerpretation will con- 
tinue to improve their techniques, the highway or tunnel engineer 
must apply these techniques, and based on his experience, must 
make contributions to the development and improvement of analysis 
techniques. However, as the paucity of remote sensing literature 
related to tunneling attests, little interest and perhaps consider- 
able skepticism surrounds remote sensing application to tunneling. 

Szechy (1970) in his book "The Art of Tunneling" mentions 
the importance of aerial photographs for studying geologic features 
including faults, folds, and rock outcrops. He also indicates 
that by analysis of vegetation types it is possible to estimate 
"gross chemical characteristics, and thus the origin (igneous or 
sedimentary) of the underlying bedrock." Szechy quotes a list of 
geologic features and tunneling conditions published by Stinni 
(1950): 



18 



1* The orientation of rock stratification (whether 

horizontal, sheet like, moderately inclined, 

steeply sloping, or over folded). 
2* The thickness of individual layers, the regularity of 

the sequence of rock layers or changes in mountain 

types. 
3* Mineralogical composition (detrimental components). 

4 The crystalline structure of rocks (uniform grains, 
porphyritic) . 

5 The bonds between the individual grains (strong, weak, 
direct, indirect). 

6* A hardness of the rocks, whether they would allow for 

drilling or blasting. 
7* The structural form of rocks (massive, stratified, or 

shaley) . 
8* The internal structure (whether solid or porous, with 

closed or open voids). 
9* Deformation suffered during the origin process (cleavages, 

joints, crushed zones, faults) or other effects (such 

as weathering, mylonitization, or koalinization) . 
10 The probable bearing and tensile strength of the mountain 

at various tunnel sections. 
n The stability of the mountain, the character and magnitude 

of probable rock pressure. 

12 The bulk densities and dead weights of component rocks. 

13 The anticipated durability of various rock types to be 
penetrated, the length of entrance sections to be lined 
with regard to the danger of frost effects. 

14 The depth and composition of cover of each point of the 
tunnel for each rock constituent. 

15 Temperature conditions affecting the mountain. 

16* Hydraulic conditions at the construction site and its 
environment. 

17 The possibility of the occurrence of harmful gases. 

18 The susceptibility of structure to earthquakes and 
artificial vibrations. 

19* Surface formations 

20 Safety against escaping air in anticipation of operations 

involving compressed air. 
21* Hazards to structures and especially to entrance portals 

by forces of nature (rock slides, rock falls, avalanches, 

or slumping) . 



19 



The work of some of the pioneers who have applied advance 
remote sensing systems and analysis techniques to tunneling, 
geology and hydrology is presented in the overview of sensors 
evaluated during this study. These sensor systems include: 

SLAR (Side Looking Airborne Radar) 

Photographic systems 

Scanning systems (multispectral and thermal) 

Airborne geophysical systems 

Imaging satellite (orbital) sensor systems 

The first imagery of the earth from satellite platforms, 
acquired in the early 1960's by the first weather satellites and 
early manned spaceflights, presaged the value of such data for 
earth resources. With increasing coverage by Gemini and early 
Apollo flights, it became apparent that a satellite devoted 
solely to the acquisition of earth resources information was 
needed. The first such satellite, known as ERTS (Earth Resources 
Technology Satellite), launched in July of 1972 not only provided 
earth resources data, but provided repetitive coverage of each 
area every 18 days. Today, a second satellite (the system is 
renamed LANDSAT) is orbiting in addition to the first, giving 
nine-day repetitive coverage. 

In four years since the launch of LANDSAT-1 , many investigators 
have described capabilities that can be of importance to tunneling. 
Some of these include identification of: lithology and lithologic 
boundaries, geologic structure, fractures, landslides, alteration 
zones, intrusions, and various geomorphic features. 

Collins et al. (1974) and Saunders (1974) noted that the 
boundaries of many surficial deposits can be mapped quite accurately, 
but that other inferred lithologic boundaries appear to parallel, 
but do not necessarily correspond with previously mapped boundaries. 
Houston (1975) and Collins et al. (1974) noted that in some 
instances it was possible to identify and revise the location of 
contacts on existing geologic maps. Miller (1975) states that 
boundaries between rock types can be traced from the LANDSAT 
images even though the nature of the lithology is not clear. He 
further states that in some instances it is possible to make some 
identification of lithology. 

Sawatzky, et al . (1975) studied the relationships of linear 
features to joint systems and large geologic structures and 
discussed techniques to extract geologic information. Other 
investigators have also discussed techniques to analyze structural 
features and lithology (Podwysocki, 1975; Goetz, 1975; and Vincent, 
1973a). MacDonald and Grubbs (1975) made an important contribution 
to highway and tunnel construction by correlating linear features 



20 



detected on LANDSAT imagery with landslide prone areas along 
major highway routes. They state: 

"The weathering properties of various rock types, which are 
considered in designing stable cut slopes and drainage 
structures, appear to be adversely influenced by the location 
and trend of LANDSAT identified lineaments. Geologic interpre- 
tation of LANDSAT imagery, where applicable and utilized 
effectively, should provide the highway engineer with a new 
tool for predicting and evaluating landslide prone areas." 

Campbell et al. (1975) has used satellite and aerial photo- 
graphy to detect lineaments for planning mine openings. Campbell 
also describes the use of this data and core boring to develop a 
geologic model of roof conditions prior to the development of an 
underground mine or major extension of a mine. He estimates that 
the labor and materials required to stabilize the roof of the 
mine openings may be 35% of the total cost of mining. Roof 
support requirements are related to geologic conditions, and 
therefore an accurate forecast of geologic conditions before 
excavation of main haulageways is essential to accurate estimates 
of mine development costs. 

In addition to LANDSAT data, high resolution black-and- 
white, color, and color infrared imagery and photography is 
available from the three manned Skylab missions which began in 
1973. Skylab photography has several advantages over LANDSAT 
data including greater spatial resolution, stereoscopic coverage, 
true color and color infrared film rather than color composites. 
One disadvantage, however, is that there is no repetitive coverage 
and areal coverage is limited. 

Several investigators (Bechtold, et al., 1975, and Sawatzky, 
et al., 1975) identified zones of alteration associated with 
mineralization. They have also described the geologic significance 
of linear features detected on Skylab photography. Amsbury et al. 
(1975) used Apollo, LANDSAT, and Skylab data as a reconnaissance 
tool for mapping geologic features including soil tones. Cassinis 
et al. (1975) have used Skylab multi spectral scanning imagery for 
hydrologic analysis. By digitally enhancing the images using a 
ratio and product algorithm and with suitable ground truth, 
Cassinis was able to identify moisture differences between soil 
types over paleo-river beds. The significance of this capability 
is that it not only predicts hydrologic conditions but estimates 
the trafficability of certain areas. 

The overall assessment of satellite acquired data is that it 
is extremely useful for identifying regional geologic structural 



21 



relationships (Abdel-Gawad, 1975, Liggett, 1974, Collins et al . , 
1974, and Wilson, 1975). 

Radar imagery has several distinct advantages over satellite 
data when it is used as a reconnaissance tool. Radar has an all- 
weather, day/night capability, it has better resolution than 
orbital data (16 to 25 meters), and stereoscopic coverage is 
available. Several authors discussed the day/night and all 
weather capability of radar imagery (Dellwig and Burchell, 1972; 
Viksne et al . , 1970; Crandall, 1969; Hackman, 1967a; Am. Soc. of 
Photogrammetry, 1975). 

The first semi-operational radar survey that generated wide- 
spread interest was conducted in 1967 over a 17,000 square kil- 
ometer area in Darien Province, Panama. This survey reported on 
by MacDonald (1969); Crandall (1969); Viksne et al . (1970); Wing 
(1971); Dellwig and Burchell (1972); demonstrated radar capa- 
bility to: obtain slope and relief data; make lithologic boundary 
discriminations; identify drainage patterns; and obtain data on 
vegetation, geologic structure, and soil moisture. Perhaps the 
most impressive capability of the radar system was the ability to 
gather this data even though the Darien Province is almost always 
cloud covered. 

Wing (1970) discusses the advantages of the synoptic view 
that radar imagery gives and the suppression of detail which 
often complicates the analysis of aerial photography. Many 
regional linear features that may have geologic significance 
often have topographic expression that is enhanced by radar 
imagery. MacDonald, et al . (1969) and Reeves (1969) discussed 
the importance and geologic significance of lineaments not previously 
mapped. Geologic analysis including identification of boundaries 
and description of rock type is possible also on radar imagery. 
"Sedimentary and volcanic rocks, their metamorphic equivalent, 
and igneous rocks may be separated from one another on radar 
imagery" (Am. Soc. of Photogrammetry, 1975). Hackman (1967) 
reported that gypsiferous and calcareous sedimentary rocks appeared 
as yery light tones of gray in contrast to darker shales and 
sandstones on radar imagery. Moore and Dellwig (1966) differentiated 
between lava flows and alluvial fan deposits based on the surface 
texture of those features. Micro-relief (surface texture) and 
surface drainage patterns can often be used to infer a lithologic 
type. Surface texture (roughness) can, however, be a function of 
vegetation; therefore lithologic determinations in vegetated 
areas may not be as reliable (Am. Soc. of Photogrammetry, 1975). 

Many authors have discussed the usefulness of radar imagery 
for analysis of drainage patterns and subsequent geologic interpre- 



22 



tation (Dellwig et al., 1968; McCoy, 1969; Gillerman, 1970; Wing, 
1970a and b, and 1971; Simonett, 1971; MacDonald, 1969). 

Several authors (MacDonald et al . , 1967; Clark 1971a) dis- 
cussed the similarities between radar and low-.sun-angle photography 
(LSAP). Hackman (1967a, b,) reported on both field and modeling 
studies with LSAP. Among other conclusions he states that optimum 
solar elevation is determined by the type of terrain. Hackman 
(1967b), MacDonald et al . (1969), and Slemmons (1969) discussed 
the importance of selecting the best solar elevation and azimuth 
for studying terrain. Terrain features of low relief require a 
lower sun angle for enhancement than do features in areas of 
higher relief. Clark (1971a, b) stated that linear features are 
best enhanced with solar azimuths nearly perpendicular to those 
linear features. Radar has an advantage in this respect in that 
the azimuth can be controlled. Clark (1971a) also states that 
radar and low-sun-angle aerial photography are not actually 
competing systems because they record information from different 
spectral bands. Lyon (1970) discusses the simulation of radar 
imagery using aerial photography and concludes that photography 
acquired at a solar elevation of approximately 27° and processed 
to increase the contrast of the prints is the best procedure for 
simulating radar. Commercially, low sun angle photography taken 
with black and white infrared film has been used successfully in 
petroleum exploration in Indonesia (Foster, 1974). 

Panchromatic (black-and-white) film is the most common type 
of film used for photogrammetric mapping. High spatial resolution, 
panchromatic film is also used for geologic structural analysis, 
topographic analysis, lithologic identification, and stratigraphic 
description (Am. Soc. of Photogrammetry, 1975). Photographs with 
a 50%-60% overlap are used for stereoscopic viewing. Topographic 
contour and structural contour maps can be drawn from stereo 
pairs. Stereoscopic models are particularly useful in geomorpho- 
logical analyses; Wolf (1974) describes the method of constructing 
stereoscopic models. Tator (1949) mapped the bedrock erosion 
surfaces based on morphological detail. Denny (1952) also used 
stereoscopic models in his studies of Late Quaternary geology and 
frost phenomenon along the Alaskan Highway. 

Aerial photographs are widely used for analysis of soil 
type, lithology, vegetation, and field mapping. For a discussion 
on the interpretation of rock characteristics based on topography, 
identification of rock type based on drainage patterns and identifica- 
tion of soil type based on erosion patterns refer to Appendix C. 

The human eye has a capability of distinguishing over a 
hundred times more color combinations than it can gray scale 
values (Evans, 1948). As a result, color photographs can yield 

23 



more information for lithologic and soil identification, which 
are largely based on color differences. Aldrich (1966) reports 
that photointerpreters can "detect significantly more targets on 
normal color imagery than on black and white photography." Soil 
surveys in the past were largely conducted using black and white 
aerial photography. However, with the improvement of color 
aerial photographic films, most soil surveys are now conducted 
using color photos. Many investigators have demonstrated the 
increased utility of color aerial photographs for soil analyses 
(Mollard, 1968; Mintzer, 1968; Rib and Miles, 1969; and Parry et al . , 
1969). Meyers and Stallard (1975), have reported that the 
combined use of thermal infrared imagery and color aerial photography 
provided the best results for identification, description and 
mapping of soil groups (Am. Soc. of Photogrammetry, 1975). Color 
infrared photography is particularly useful in vegetation analyses. 
By the use of color infrared imagery, plant species can be differenti- 
ated, vigor of the vegetation can be determined, and in some 
cases, stress conditions can be inferred (Fritz, 1967). 

When conducting aerial photographic surveys, it is helpful 
to visit the site at least twice; once before the survey, to plan 
flight lines and to make a general geologic analysis, and a 
second time after the imagery is acquired and after an initial 
interpretation is made, to verify interpreted features and to 
investigate areas that cannot be satisfactorily interpreted on 
the aerial photographs. Reed (1940) suggests that final verification 
be accomplished using aerial photographs by marking places on the 
photograph where strike and dip measurements are made, and where 
faults and lithologic contacts are located. 

Multi-band photography and multi spectral scanning are in 
principle the same investigation technique. In practice, one is 
a photographic system and the other is an optical-mechanical 
system. Many authors have discussed the application of multi- 
band (multispectral) analysis to geologic mapping (Coker et al., 
1969; Fischer 1960, 1962; Meier et al . , 1966; Myers and Allan, 
1968; Paarma et al., 1967; Paarma and Talvitie, 1968; Pestrong, 
1969; Pohn et al., 1972; Tarkington and Sorem, 1963; Vincent, 
1972a; Yost and Wenderoth, 1968, 1972). 

Many investigators have made attempts to use expected or 
empirically derived spectral signatures to differentiate, and 
where possible, identify various rock and soil types. Two important 
studies have approached the task of identifying spectral responses 
of rocks, soils, and vegetation on a comprehensive scale. Hunt, 
Salisbury, and Lenhoff (1970-1974) have published a series of 
papers about the spectral characteristics of minerals, rocks, and 
soils in the visible and near-infrared portion of the electro- 
magnetic spectrum. Their nine papers, to date, have examined: 



24 



I. Silicate Minerals VI. Additional Silicates 

II. Carbonates VII. Acidic igneous rocks 

III. Oxides and Hydroxides VIII. Intermediate Igneous 

Rocks 

IV. Sulphates and Sulfides IX. Basic and Ultrabasic 

V. Halides, Phosphates, Igneous Rocks 
Arenates, Vanadates, Borates 

The second study is the NASA Earth Resources Spectral Informa- 
tion System: "A Data Compilation," V. Leeman et al., 1971. This 
report and its supplements include "bi-directional and directional 
reflectance, transmittance, emittance, and degree of polarization 
curves in the optical region from 0.2 - 22.0 m" for rocks and 
minerals, soil, and vegetation. The NASA Earth Resources Spectral 
Information System is intended to provide a data base with which 
remote sensing techniques can be used to identify and describe 
surface features. Other investigators have analyzed spectral 
responses on a more limited scope. The identification and descrip- 
tion of rocks, minerals, and soils using remote sensing techniques, 
however, cannot be completely accurate in most instances without 
field verification. 

Atmospheric interference is a major factor accounting for 
the differences between the spectral response of a specimen in 
the laboratory and in the field. In the "Manual of Remote Sensing" 
(Am. Soc. of Photogrammetry, 1975) an entire chapter is devoted 
to atmospheric effects on remote sensing. They state that the 
characteristic spectral response of many materials under one set 
of environmental conditions may be different from the response 
under another set of conditions. Reflected and radiant energy is 
absorbed, scattered, and otherwise attentuated by the atmosphere 
depending on the temperature, type and concentration of atmospheric 
particulates, percent cloud cover and cloud height. 

Another factor that accounts for different responses of 
identical specimens between the laboratory and field is background 
or field-of-view interference (Egbert, and Ulaby 1972). In the 
laboratory under controlled conditions, the energy received by the 
sensor comes only from the specimen or specimens and a uniform 
background. In the field, a rock type, for example, might occur in 
isolated points within the field-of-view. The background in this 
case may not be uniform and may contribute energy that could 
amplify or attenuate the energy emitted by the rock. This altera- 
tion of the spectral response could be sufficient to cause a mis- 
identification of the rock type. 

The illumination of a specimen in the field is significantly 
different from laboratory illumination. In the laboratory the 
prime source of illumination may or may not be spectrally the 
same as solar illumination in the field. Surfaces surrounding 
the target in the field and laboratory reflect light, which in 

25 



turn, is incident upon the target. The effect of additional 
energy reaching the speciman from other reflecting surfaces is to 
alter the spectral response of the speciman. Reflected energy 
from clouds or the sky is also received by the target and has a 
similar modifying effect (Piech and Walker 1971a and b). 

Another difference between laboratory and field analysis of 
spectral response arises when the response of a fresh rock surface 
is used as a standard for field targets. In the field the surfaces 
of rocks are contaminated by weathering products, lichen, desert 
varnish, soil or dust, and solution deposits of various minerals. 
All of these can radically influence the spectral response. This 
source of difference is not so difficult to control as varying 
illumination because the contaminated surfaces can also be tested 
in the laboratory. The composition of rocks, minerals, and soils 
using remote sensing techniques cannot be entirely based on 
expected spectral response of a standard or standards. 

Gilbertson and Longshaw (1975) conducted an extensive evalua- 
tion of multispectral aerial photography as an exploration tool. 
Their approach was to: 

• Measure the spectral response of rocks "in situ." 

• Select photographic filters that will enhance a character- 
istic spectral response based on the "in situ" measure- 
ments. 

• Obtain "quantitative aerial photography." They use the 
phrase "quantitative aerial photography to mean that 
ground objects receiving the same solar irradiance and 
possessing the same spectral reflectance properties are 
imaged at the same density on every frame of the final 
separation positive stage." 

• Use additive color techniques to interpret the imagery. 

Their "results indicated that the multispectral photography 
enhanced spectral differences between object categories and 
displayed geologic context more distinctly than other imagery. 
However, both features were also well represented in either the 
color or false color infrared photography. On this basis it was 
concluded that the additional complexity and costs involved in 
the multispectral approach to aerial photography was not justified." 

Rains and Lee (1975) concluded after statistical analysis of 
over 8,000 measurements of sedimentary rocks made in the field 
with a photometer and a series of Wratten filters, which spanned 
the visible and near-visible portions of the spectrum: "No 
practical numerical basis exists for selecting any particular 
spectral band as best for rock discrimination, and in most instances 

26 



little numerical basis exists for selecting better spectral 
bands." Therefore, information useful for the design of multiband 
photography cannot be obtained from the type of "in situ" spectral 
measurements considered here. Though this may be true, whatever 
the spectral response of a target, once this response has been 
associated with that target it can be used in most situations to 
identify the target material elsewhere on the image. This spectral 
response, however, may be valid only for the specific time and 
place of the image. The application of the response to the 
analysis of imagery acquired on another day or in another location 
may not be valid. 

Lowman (1969) and Lyon (1971) have reported that geologic 
analysis including description of structure and differentiation of 
soil and rock type using multiband (multispectral) techniques are 
more effective when these features are associated with vegetation. 

Piech and Walker (1971a, b, 1972a, b, 1974) described positive 
results using multiband techniques. They developed a technique 
called "Scene Color Standard" which removes "peripheral effects" 
such as "source effects, atmospheric effects, and surface reflec- 
tions" (primarily skylight reflection). This technique is applied 
to a ratio display (Smith, Piech, Walker 1974). Briefly, the ratio 
analysis is performed by making color separations from true color 
aerial photographs. The positive and negative transparencies of 
these separations from different bands are superimposed under a 
vidicon tube. The ratio pair is then density sliced by assigning 
different colors to subtle gradational changes throughout the 
image. The resultant image is displayed on a color cathode ray 
tube (CRT) for study or for photographing a permanent record. 

Using this technique it is possible to identify differences in 
soil moisture and textural patterns. This technique promises "More 
precise aerial survey classification of engineering properties such 
as drainage class, void ratios, structure and bearing strength with 
further study" (Piech and Walker, 1972b). 

The application of the ratioing techniques of two-channel 
thermal infrared data (8-1 4ym) to soil and rock discrimination has 
been discussed by Vincent et al. (1973), Vincent and Thomson 
(1972a), and Vincent et al. (1973). Using this technique, it is 
possible to discriminate between different types of silicate 
rocks. In their work at Pisgah Crater, California, Vincent and 
Thomson (1972a) reported that "dacites and basalts were clearly 
discriminated and were identified on the basis of their thermal 
ratio values." Vincent et al. (1973) have also applied ratioing 
techniques to soil analysis. They conclude that "soil color, 
terrain patterns, natural drainage, and soil texture are enhanced 
by ratio images. " 



27 



Rowan and Cannon (1970) were able to differentiate limestone, 
dolomite, and granite during their work in Mill Creek, Oklahoma. 
From stratigraphic analysis based on this discrimination capability, 
they noted that topography has an important influence on the 
thermal emissivity. The sunlit side of a landform provides better 
stratigraphic information. 

Another capability of thermal infrared images reported on by 
Rowan et al. (1970) is the delineation of faults and fracture 
zones. They attribute the detectability of these features to zones 
of soil moisture. They also note that these zones are not visible 
on conventional aerial photography. Other investigators (Sabins, 
1969; Offield et al., 1970; and Wallace and Moxham, 1967) have 
reported similar results in lineament and fracture mapping using 
thermal imagery. 

Although significant results have been reported and promising 
areas of future research identified for thermal imagery, most 
investigators will agree that these techniques must be used in 
conjunction with aerial photographic data and field analysis. 

Extensive work has been done using airborne geophysical 
techniques. The two most common techniques are magnetic and 
electromagnetic surveys. The airborne magnetometer was developed 
during World War II as a submarine detection system. Following the 
war it was modified and applied to petroleum, and somewhat later, 
to mineral exploration (Hansen et al . , 1967). Magnetic surveys 
measure the earth's magnetic field and perturbations or anomalies 
of the earth's magnetic field caused by varying concentrations of 
the common mineral, magnetite. This concentration can in turn be 
"interpreted in terms of rock type and geologic structure," 
(Strangeway, 1967; Am. Soc. of Photogrammetry, 1975). Because some 
rocks are more magnetic than others they can iDe differentiated and 
the approximate contacts between them located (Strangeway, 1967; 
Isaacs, 1967). The size, shape, and general structure of the 
recorded anomalies can be used to infer the shape, depth, and 
composition of the bodies causing the anomaly (Isaacs, 1967; 
Smelli, 1956; and many others). The shapes may be determined by 
faulting, intrusives, mineralization, folds, and flows. Other 
larger scale structural features can also be detected such as 
basins and domes. Thus, airborne magnetic surveys can provide 
considerable information on the structural features and distribu- 
tion of rock types within a given area. 

Electromagnetic systems measure the conductivity of subsurface 
formations. A transmitter produces an electromagnetic field which 
extends through the rock according to the conductivity of the rock. 
The signal is modified by the rocks and returned to the receiver. 
The most influential factor in the electrical characteristics of 
rocks and unconsolidated earth materials in the upper or near- 
surface zone is the free water in the fractures and pores. This is 

28 



especially the case at the ultra low frequencies (less than lO^Hz) 
normally used in geophysical techniques in order to achieve sig- 
nificant depth of exploration. 

The subject of the influence of pore water on conductivity has 
been treated by several authors, both experimentally and theoreti- 
cally. Representative data are found in the papers by Zablocki 
(1962), by Keller (1963, 1971), and particularly those by Brace 
(1965, 1968a, b, 1971), Parkhomenko (1960 and 1967), and by Levin 
(1966, 1968, and 1971). The subject is treated by Ward and Fraser 
in Chapter II, Part B, "Conduction of Electricity in Rocks", in 
Volume II of Mining Geophysics (1967). Keller (1963) graphs the 
resistivity of waterbearing sandstones as a function of frequency 
and water content at 20°C; at IKHz the resistivities range 1^rom 
lO^ohm/m for 3.5% water content to 10^ ohm/m for 53% water. In 
Parkhomenko's textbook Electrical Properties of Rocks (1967), 
similar data are given for a variety of sedimentary, metamorphic and 
igneous rocks. In a coarse grained sandstone, for example, slight 
variations of water content from 0.18% to 0.34% causes the con- 
ductivity to increase from 10-8 mho/m to lO-^mho/m. In another 
example the conductivity of dolomite ranges over 5 decades of 
magnitude as the moisture content varies only from 0.1% to 1.0%. 

Traditionally, airborne resistivity techniques have been used in 
the search for metal deposits ( Mining Geophysics Vol. I and II, 
1967). The application of airborne resistivity techniques to 
detecting differences in the pore-water content of near surface 
rocks and fractures is a relatively new field of endeavor. Fraser 
(1972a and b; 1974), Hoekstra and MacNeill (1973), Hoekstra et al . 
(1975), Culley et al. (1975), Dyck et al . (1974), and Sinha (1973) 
describe some of these efforts and results. Based on these works it 
appears that airborne resistivity methods have considerable poten- 
tial for detecting conductive zones such as shear zones, sink holes 
and cavernous limestones, conductive overburden etc., of interest to 
tunnel site investigation. Under many sets of conditions it is 
possible to infer the orientation of these bodies (Fraser, 1972 a 
and b, 1974) using the Dighem system. 



4.2 Tunneling Conditions and Significant Geologic Features 

Engineers involved with the planning and execution of tunnel- 
driving operations are primarily concerned with the excavation 
characteristics of the ground and the behavior of the ground during 
and after excavation. The method of excavation, the construction 
schedule and the estimate of construction costs rest on an engi- 
neering appraisal of the following operational considerations: 



29 



a. Is the most suitable method of excavation hand spading, 
drilling and blasting or machine boring? 

b. Will the tunnel face be stable enough to excavate the 
full cross section of the tunnel in a single operation 
or will the ground require top heading and bench or 
multiple-drift excavation? 

c. Will the tunnel walls stand without support or will it 
be necessary to install an initial support system 
comprised of rock bolts, shotcrete, steel ribs and 
lagging or linear plates? 

d. Will the tunnel encounter dry, moist or wet material 
and will it be necessary to provide pumping capacity to 
maintain working conditions? 

e. Will the ground exposed in the tunnel bore be stable or 
will it deteriorate because of swelling, air slaking, 
or stress-relief fracturing? 

f. Will the rocks exposed in the tunnel bore produce toxic 
or explosive gasses, requiring special safety procedures? 

The term "tunneling conditions" is used in this report to 
collectively refer to those characteristics of the ground and the 
tunnel which directly affect the tunnel-driving operation. 

Geologic science provides the knowledge and techniques to 
make a major contribution to a preconstruction evaluation of 
tunneling conditions. Geologic studies identify natural materials; 
divide these materials into units which can be mapped and projected 
on the ground surface and the subsurface; and provides a basic 
understanding of the origin and history of the materials. The 
end product of the geologic study of a site is a picture or model 
of the geologic conditions developed from incomplete information. 

Tunneling conditions cannot be directly assessed from even 
the most complete and accurate model of geologic conditions for 
several reasons. First, the model of geologic conditions is 
limited to the composition and the geometric characteristics of 
the ground and does not provide information about the behavior of 
the ground in a tunnel opening. Second, experience has shown 
that geologically identical materials behave differently depending 
upon factors such as tunnel depth, the groundwater head over the 
tunnel, the cross section of the tunnel, and the method of excavation, 
The tunnel conditions may be determined from the geologic conditions 
model by using experience in similar tunnels in similar geologic 
environments or by using soil mechanics and rock mechanics analysis 
techniques. 



30 



This report is concerned with the collection of geologic in- 
formation for the geologic conditions model and specifically with 
the application of remote sensing methods in these investigations. 
The best test of the application of remote sensing is the capability 
of these methods to locate or measure those geologic features that 
generally affect tunnel construction. 



4.2.1 Significant Geologic Features 

Tunnel site investigations are principally or essential- 
ly geologic studies with the specific goal of defining the 
geologic conditions that may affect the construction of the 
tunnel. The investigation should be designed, executed and 
documented so as to efficiently and economically reach this 
goal. Almost any geologic feature may be significant under 
certain circumstances, but many of the geologic details that 
are included in scientific reports on geology are of limited 
value in this context and may be confusing to the non-geologic 
readers. For example, the fossils present in sedimentary rocks 
is a normal and often major part of a geologic report on an 
area underlain by sedimentary rocks, but the fossils present 
deserve little consideration in a tunnel site investigation 
unless the fossils help to define the bedrock structure. The 
same argument for limiting geologic detail can be applied to 
small-scale structures or the detailed petrology of sedimen- 
tary, metamorphic or igneous rocks. 

The term significant geologic features refers to those 
features, or classes of features, which commonly affect the 
construction of a tunnel: 

Soil and Rock Type * Ground Stresses 

Alteration * Ground Temperature 

Geologic Structure * Hazardous Gases 

Discontinuities * Earthquakes 
Groundwater 

These features are briefly described in the following 
paragraphs. 



4.2.2 Soil and Rock Type 

Soil type, as determined from either the simple grain- 
size classification of gravel, sand, silt, and clay or the more 
specific Unified Soils Classification system, provides a useful 
indication of the general engineering characteristics of the 
soil mass and a general indication of soil behavior in a 

31 



tunnel. Soil type alone indicates a range of permeability, 
strength and compressibility, the relative stability of the 
soil in tunnel opening and whether groundwater control will be 
an important aspect of construction. Although these judgments 
need verification by other information and definition by 
testing, the soil type is an excellent starting point for 
appraising tunneling conditions. 

The geologic classification of rock, based upon miner- 
alogy and grain size, is less helpful than soil classification 
in assessing tunneling conditions. Some rock types such as 
granite suggest a reasonably limited range of hardness, 
stability, and groundwater conditions to be helpful but in 
most instances the subsurface conditions are not so specifi- 
cally related to rock type. Shale is an extreme example of a 
rock name applied to substances with widely varying physical 
characteristics. Shale may be hard or soft, stable or wery 
unstable, and highly compressible or moderately compressible. 
Rock type, therefore, is a worthwhile starting point in 
describing a rock mass but is rarely totally diagnostic of the 
rock mass. 



4.2.3 Alteration 

Although geologic materials often appear to be imperish- 
able, most will change if removed from the temperature, 
pressure, and chemical environment in which they were formed. 
Under new conditions the mineralogy and the physical proper- 
ties will change until an equilibrium has been established 
with the new environment. Alteration is the term which is 
applied to all these changes whether they occur at the ground 
surface or at depth in the earth's crust. Of particular 
interest to tunneling are those changes that occur near the 
ground surface where soil and rock is exposed to weathering 
and those changes that occur at depth due to the presence of 
hot aqueous solutions. 

The term weathering is applied to a host of physical 
and chemical changes caused by air and chemically-active 
groundwater. The reactions include solution, oxidation, 
carbonation and hydration. Weathered zones are generally 
found in the soil and the upper portions of the bedrock but 
ancient weathered material is sometimes encountered deep 
within the bedrock. Weathered material generally has less 
strength and cohesion than the unweathered host material. 
Weathered bedrock, for instance, may retain the structure of 
the host rock but have the properties of a soil. The depth of 
weathering is quite variable depending upon the climate, rock 
type, and the permeability of the host material. Evidence of 

32 



weathering in bedrock is often found along joints tens to 
hundreds of feet below the top of rock and can affect the 
behavior of the rock mass at tunnel level. 

High temperature solutions of water and gas rise from 
magma sources in the earth's crust along faults and fracture 
zones. These solutions react with the cooler host rock, 
locally form ore deposits and more generally change both the 
mineralogy and the physical properties of the host rock. In 
some instances the alteration seals fracture zones and im- 
proves the bearing strength of the rock mass but these changes 
also create rock mass conditions that are unfavorable for 
tunneling purposes. These zones are difficult to locate and 
evaluate prior to tunneling if the depth of cover is great. 



4.2.4 Geologic Structure 

Geologic structure is the geometric arrangement of rock 
units and zones of discontinuity. In geology this term is 
applied to features such as folds, faults, unconformities, 
instrusions, joints, cleavage, and schistosity on a scale 
ranging from hundreds of miles (mega- lineaments) to the field 
of view of a microscope. 

For the purposes of tunnel site selection and evolution, 
one generally can ignore microscopic features (they are 
considered properties of the rock material) and the mega- 
lineaments unless a fracture that is part of this major 
feature is present at or close to the site. Curiously, mega- 
lineaments are so large that they are difficult to recognize 
on the ground or in large scale air photographs, and yet many 
of them can pose major problems to tunnel construction in the 
form of major shear zones or seismically hazardous areas. 
These large features must be considered when selecting the 
highway route and tunnel site. Features such as unconformi- 
ties, joints, cleavage and schistosity are considered sepa- 
rately under the term discontinuities to indicate their 
special significance to tunneling. Faults are considered both 
a discontinuity to indicate their importance as a rock defect 
and a structural feature to account for their influence on the 
distribution of rock units. 

The geologic structure of a site is the spatial arrange- 
ment of the rock units. This spatial arrangement is of vital 
interest because the rock at the surface is normally only 
partially exposed and the rock at tunnel level is normally 
poorly explored prior to tunnel excavation. The arrangement 
of the units disclosed by incomplete information is a funda- 
mental part of the interpretation of the geologic conditions. 

33 



4.2.5 Discontinuities 

Essentially all rock masses and some soil masses 
contain fractures or zones of weakness which affect the 
engineering properties of the ground and the behavior of the 
ground during tunneling. These features are collectively 
referred to as discontinuities in this report. In rock, the 
discontinuities range in size from major faults, zones of 
sheared and crushed rock many tens of feet wide and many miles 
long, to microscopic fractures in the intact rock material. 
Most numerous are fractures known as joints which are typi- 
cally less than an inch thick and long enough to cross the 
tunnel excavation. Discontinuities usually cause the rock 
mass to have a strength considerably lower than the strength 
of the intact rock material and also cause the rock mass to 
have a compressibility and permeability considerably higher 
than that of the constituent intact rock. At many sites the 
discontinuities affect the properties of the rock mass to such 
a high degree that the properties of the intact rock materials 
are of limited practical significance. 

The pattern of discontinuities is usually complex and 
varies with location in the ground. Fortunately, the pattern 
can often be approximated by three to five sets of parallel 
discontinuities with a nearly constant orientation. One of 
the discontinuity sets is normally along the bedding in 
sedimentary rocks, the banding in igneous rocks or the folia- 
tion in metamorphic rocks. The orientation of the remaining 
sets depends upon the stress history of the rock mass. 

The behavior of ground in the tunnel is difficult to 
assess because the pattern of the discontinuities is only 
partially defined during the tunnel site investigation and the 
properties of individual discontinuities may vary considerably 
with the detailed characteristics of the feature. Some of 
the more important characteristics of discontinuities are: 
orientation of the discontinuity with respect to the tunnel 
opening; orientation of the discontinuity with respect to 
other sets; spacing; thickness, character of the filling 
material; geometry of the opposing surface of intact rock; 
properties of the intact rock; and hydrostatic pressure. Any 
information which improves the pre-construction knowledge of 
the pattern or characteristics of the discontinuities would 
improve pre-construction assessments of tunneling conditions. 



4.2.6 Groundwater 

A tunnel is a horizontal well which can drain ground- 
water and even surface waters. The quantity and rate of water 

34 



inflow and the duration of inflow depend upon the local 
hydrologic conditions including the hydrostatic head, the 
length of available flow paths, and the permeability of the 
material around and above the tunnel. 

Water inflows affect the tunnel operation in several 
ways. First, water inflows in either soil or rock can bring 
soil material into the tunnel that presents a cleanup problem 
and more importantly tends to weaken the surrounding ground. 
The loss of a relatively small amount of solid material can 
turn otherwise stable soil or rock into unstable ground which 
requires heavy support. Sometimes inflows lead to a sub- 
sidence of the tunnel cover that extends to the surface. 
Large quantities of water inflow present a tunnel dewatering 
problem which sometimes forces a shutdown of the tunneling 
operation. Small quantities of inflow are generally only a 
nuisance unless the ground exposed in the tunnel walls and 
tunnel floor soften upon exposure to water. Inflows of water 
can also deplete groundwater storage to the extent that neigh- 
boring wells go dry and surface water supplies are affected. 
Finally, chemically active groundwater can cause damage to the 
tunneling equipment, steel supports and concrete within the 
tunnel. 

The presence of water-bearing strata, the location of 
the groundwater table, the potential hydrostatic head at 
tunnel level and the general permeability of the ground can be 
determined during site investigations. However, the quantity 
of inflow and the duration of inflow are difficult to estimate. 



4.2.7 Ground Stresses 

Geologic studies provide evidence that the stress 
conditions near the ground surface are complex. This evidence 
includes active faulting, fold structures formed at apparently 
shallow depths, and joint systems which indicate the presence 
of high horizontal stresses near the ground surface. Rock 
bursts in strong, brittle rocks in quarries and shallow mines 
provide additional evidence that the stress conditions present 
in the rock do not always reflect the existing overburden 
weight. 

Techniques developed in recent years to measure the 
rock stresses around underground openings and in borings have 
confirmed the presence of stress conditions that are anomalous 
with respect to existing overburden. Vertical and horizontal 
stresses both higher and lower than overburden weight have 
been noted. These measurements indicate that anomalously high 



35 



horizontal stresses are more common than would have been 
suggested from geologic evidence alone. 

Anomalous stress conditions are an important factor to 
be considered in the design of final support systems, particu- 
larly in large underground openings. The stress conditions 
may also be important in the design of the initial support and 
in the selection of tunneling methods in those geologic con- 
ditions where rock bursts may affect the safety of the work. 



4.2.8 Ground Temperature 

The air temperature in underground openings near the 
ground surface seems lower than the air temperature outside, 
but the ground temperature is actually close to the mean 
annual air temperature. At greater depths the ground tempera- 
ture normally increases about one degree Fahrenheit (1.8°C) 
per hundred feet. Fortunately, rock with an uncomfortably 
high temperature is well below the depth of most tunnels. 

High ground temperatures at tunnel depth are, however, 
encountered in some areas. Hot springs, geysers and recent 
volcanics are obvious surface evidence of anomalous tempera- 
ture conditions. High temperatures, however, are sometimes 
encountered in areas that lack surface evidence of anomalous 
temperatures but are actually underlain by hot, igneous 
masses. 

Moderate ground temperatures may have little influence 
on the tunneling operation but high ground temperatures may 
control the method of tunneling and the progress and cost of 
the work. The combination of high temperature and high 
humidity decreases the efficiency of the workmen and this 
leads to excess fatigue and safety problems. Under extreme 
temperature conditions, cooling sprays, refrigeration, and 
shortened working hours may be necessary to cope with the 
adverse tunnel environment. 



4.2.9 Hazardous Gases 

Toxic and explosive gases are a frequent hazard in the 
mining industry because mineral and coal deposits are commonly 
associated with high concentrations of natural gases. Haz- 
ardous gases are less frequently encountered in tunnels driven 
for civil engineering purposes because these tunnels are 
generally shallower and less frequently associated with gaseous 



36 



conditions. However, significant quantities of toxic gases 
such as hydrogen sulfide, sulfur dioxide and carbon dioxide 
and explosive gases such as methane are an operational problem 
at some sites. 

Ventilation is the primary means of controlling hazard- 
ous gases in a tunnel. Evidence of hazardous gases obtained 
during the tunnel site investigation provides a warning that 
the ventilation system should be designed for the removal or 
dilution of the natural gases, rather than the less stringent 
requirements of simply supplying filtered air for workmen and 
equipment. Advance warning of the presence of explosive gases 
may be used as a basis for specifying the use of explosion- 
proof electrical equipment in the tunnel. While gas monitor- 
ing is normally performed regardless of the evidence collected 
during the site investigation, the previously undetected 
presence of hazardous gas during the tunneling operation 
presents a safety hazard and may delay the tunneling work. 



4.2.10 Earthquakes 

Tunnels are more resistant to earthquakes than most 
other civil engineering structures, but there is still the 
possibility that strong earthquakes may lead to offsets along 
active faults, damage to or collapse of the lining, and land- 
slides at the portals. Evidence of recent strong earthquakes 
at the site may become an important element of the tunnel 
design and, to a lesser extent, this information may be used in 
construction planning. Tunnel alignments are normally se- 
lected to avoid active faults. If an active fault must be 
crossed, the crossing may be enlarged to accomodate future 
movements. 

The tunnel lining and the slopes in portal cuts are 
designed to minimize damage during earthquakes. In some 
instances the sequence of construction and the method of 
supporting the ground prior to the installation of the final 
tunnel lining may be selected so as to minimize damage and 
construction delays caused by earthquakes. 



4.3 Airborne Remote Sensors Considered and Systems Selected 
for Tunnel Site Investigations 

The proliferation in recent years of techniques of remote 
sensing of the ground environment using active and passive methods 
would lead one to believe that state-of-the-art devices are avail- 
able to determine most engineering parameters of the terrain. Even 

37 



if this were true, considerations such as cost/quality trade offs, 
availability, and time interact to restrict the number of sensors 
one should use on a particular project. 

During the planning phase of this study, sensing devices 
covering the electro-magnetic spectrum from very low frequencies 
(VLF) to gamma radiation (Figure 1) and force fields for applica- 
tion to tunnel site surveys were considered. 

Many sensors, including radiometers, scatterometers , active 
and passive scanner imaging systems, reflectivity sensing devices 
and force field sensors, have demonstrated capabilities in the 
detection of ground characteristics under various conditions. With 
sensors covering such a wide spectrum, differences in emissivity, 
absorption, scattering, penetration, and resonances can be of value 
in discriminating and identifying terrain and surface features. 
Polarization phenomena, stereoscopic techniques, and multispectral 
analysis methods, such as those used with imaging and reflectivity 
devices, can be exploited as additional means for discrimination. 

Significant surface penetration of up to several feet can be 
achieved with sensors that operate at the longer wavelengths (3 
feet; 1 meter; or greater) or with force field sensors; therefore 
it is possible to obtain information bearing on subsurface layering 
and terrain composition with appropriate instrumentation. 

Radiometers operate from the long wavelength end of the 
microwave spectrum into the micrometer region. These devices can 
provide information on the thermal state of the terrain, certain 
physical constants, small scale surface roughness, and soil mois- 
ture data. 

Coherent and noncoherent imaging radar systems generally 
operate in the X- and K-band regions of the microwave spectrum. 
Commercially available real aperture (brute force) and synthetic 
aperture or coherent systems have azimuth and range resolutions of 
better than 30 feet (10 meters), and produce relatively high 
quality radar maps of the terrain. Such maps are a valuable 
adjunct to aerial photographs for tectonic analysis (especially 
fracture analysis) in the study of hydrology, structural geology, 
and in lithologic distribution. 

Thermal infrared sensor systems (i.e., infrared spectroradio- 
meters and infrared scanner systems) sense emitted energy in the 
3.5-5. 5ym and 8-14um spectral range. Spectroradiometer measure- 
ments of rock types show characteristic response curves for certain 
lithologies, particularly in the 8-14ym region of the spectrum, and 
are useful for remote differentiation and identification of rock 
types. Thermal scanning devices produce thermograms ("thermal 
images") of the terrain. Because available detectors are sensitive 
to a small fraction of a degree, subtle differences in emitted 

38 




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39 



energy can be mapped to provide information about rock boundaries 
and moisture content. Digital processing of two or more appropriate 
spectral bands can produce information on iron and silica content 
of the imaged rock. 

Visible and near-visible light sensors are some of the oldest 
and most highly developed systems. There are numerous cameras, 
films, and scanner systems that can sense narrow bands in this 
portion of the spectrum. Appropriate analysis of data from these 
instruments can provide detailed information relating to a wide 
variety of disciplines. 



4.3.1 Sensor Criteria and Airborne Sensor Selection 

With the wide variety of instruments available, a major 
problem in the development of an airborne remote sensing 
system for tunnel site evaluation is the choice of the indi- 
vidual sensors in conjunction with the specific airborne 
platforms utilized and their integration into a cost effective 
operational system. 

Criteria for evaluation of sensor systems appropriate 
for providing data for tunnel site selection and evaluation 
include: 

Significance of data to tunnel site evaluation 
Availability and reliability of instrumentation 
Compatibility with related sensors 
Avionics and installation requirements 
Amenability of data to computer analysis 

The primary criterion, of course, is the sensor's 
ability to provide data needed for tunnel site evaluation. In 
selecting the airborne instrumentation package suitable for 
assessing the geologic and engineering properties of under- 
lying terrain it is necessary to consider the engineering data 
requirements. 

A second criterion is the availability and reliability 
of the instrumentation. Ready comnercial availability and 
proven flight reliability of the instruments are critical for 
cost effectiveness and practical applicability. 

In selecting an airborne system, certain compromises 
are required to achieve compatibility in the choice of air- 
craft and the desired mode of survey. It is impossible to 
operate all appropriate systems simultaneously in a single 
survey. Therefore, it is necessary to conduct multiple 



40 



overflights at different times and altitudes. In some in- 
stances several aircraft are necessary. 



4.3.2 Airborne Remote Sensing Systems 

The following discussion describes the general function 
of the various sensors and evaluates their potential applica- 
tion to tunnel site investigations. 

Gamma Ray Spectrometry 

A gamma ray spectrometer, which measures the gamma rays 
emitted by radioactive minerals, has a certain amount of 
application to identification of rock types. This is based on 
the fact that acidic igneous rocks show a higher radioactive 
potassium content than the more basic rock types. Character- 
istic uranium-thorium ratios and uranium-potassium ratios can 
also be identified for different rock types. Similarly, the 
soils derived from these rocks will exhibit the mineral com- 
position of the underlying rocks. The gross resolution and 
limited discrimination of this sensor offer only marginal 
benefit to tunnel site evaluation, and it was not incorporated 
into the study. 

Ultraviolet Imagery 

Ultraviolet imagery can uniquely identify certain rock 
and soil types. Preliminary work has indicated that carbonate 
and phosphate rock types show characteristic spectral features 
in the UV range which make them easier to identify than in the 
visible range. Aerial photography has been obtained in two 
narrow bands in the UV using a camera having a quartz lens and 
interference filters centered in the UV, but because of the 
low light levels present in the UV, a long exposure time, and 
precise image motion compensation are necessary to obtain 
sharp pictures. Multi spectral scanners with electronic ampli- 
fication have simplified source data acquisition problems, but 
poor signal-to-noise ratio and low resolution due to atmo- 
spheric diffusion and attenuation limits the value of data 
from this portion of the spectrum for tunnel site evaluation. 
For these reasons no special effort was made to acquire ultra- 
violet imagery. However, one band of UV data (.38ym) was 
acquired during the multispectral scanning survey, but did not 
make a significant contribution to the study. 

Metric Camera 

Until very recently, aerial surveys for civil engineer- 
ing applications have relied largely on black-and-white 

41 



metric frame photography. The reasons include the need for 
geometric fidelity, the better resolution achieved with 
black-and-white panchromatic film compared with color film, 
the relative ease of black-and-white film processing, and the 
adaptability to photogrammetric stereoscopic plotting. 
Although black-and-white metric photography may continue to 
provide the data base against which other data can be cor- 
related, it was necessary to evaluate conventional color and 
color infrared photography of various scales for site in- 
vestigations. 

Color aerial photography, both natural color and color 
infrared, should make an important contribution to tunnel site 
investigations. Not only can they provide quantitative topo- 
graphic data, but can also contribute to the evaluation of the 
stratigraphy, structure, hydrology, and indirectly to the 
petrology of the area. 

For regional evaluation of the tunnel sites, small 
scale color infrared photography, due to superior haze pene- 
tration properties, was considered of greatest utility. At 
scales larger than 1:12,000, natural color photography com- 
plements color infrared photography; therefore both film types 
should be used. 

Low-Sun-Angle Photography 

Low-sun-angle photography (LSAP) combines the high 
resolution and geometric fidelity of metric camera photography 
with the "shadow" enhancement capability of radar (SLAR) to 
highlight topographic features. Virtually any aerial camera 
can acquire LSAP by using panchromatic or black-and-white 
infrared film with a deep red filter. To duplicate the low 
angle of illumination characteristic of SLAR, imagery is 
acquired during the early morning or late afternoon or in the 
midwinter so that the sun elevation is between 10° and 30°. 
This produces a high contrast image with strong shadow effects 
that emphasize geomorphic features which may be related to 
geologic structure. Textural characteristics of particular 
rock types and linear topographic features associated with 
fractures are emphasized (Lyon, et al . , 1970). 

LSAP does not offer the complete freedom to select 
illumination directions that SLAR does. However, by choosing 
the time of year and the time of day, one can acquire LSAP 
photography in the northern temperate zone with illumination 
directions that range about 70° to 290° right azimuth. The 
potential of this type of imagery, plus the relatively low 
cost of acquisition, make this photographic technique worthy 
of inclusion in this investigation. 



42 



Multiband Cameras 

Multiband (or multispectral ) aerial photography uses 
several film-filter combinations to obtain a spatially coin- 
cident set of photographs in different bands of the spectrum. 
This technique can cover the near ultraviolet, visible, and 
near infrared portion of the electromagnetic spectrum. The 
short wavelength limit of spectral sensitivity is approxi- 
mately . 26ym because of ozone absorption in the atmosphere. 
The long wavelength limit is at .98ym imposed by the current 
limit of spectral sensitivity of available practical photo- 
graphic emulsions. 1/ 

The atomic lattice structure and molecular arrangements 
of materials cause them to absorb, transmit, and re-radiate 
incident electromagnetic energy at characteristic wavelengths, 
intensities, and/or polarization. Surface characteristics 
cause diffuse or specular reflection as well as polarization 
changes. A difference in spectral reflectance of objects is 
detected as images of different density on a set of multi- 
spectral photographs. To insure that this density difference 
is in fact caused by the difference in spectral reflectance of 
the object on the ground, the camera system should be spectro- 
photometrically calibrated, the spectral distribution of the 
illumination should be known, the spectral bands covered by 
each photograph should be correctly chosen, and the film 
processing should be precisely controlled. Under such con- 
ditions it should be possible to obtain image densities which 
can be related accurately to the spectral reflectance of the 
object. Photography acquired in certain spectral intervals in 
the visible and near infrared, when acquired with suitable 
film-filter combinations, is a useful tool in the discrimina- 
tion of surficial geologic character. 

It is desirable to evaluate such a system in order to 
determine if the data derived might eliminate the need for 
more complex, expensive multispectral scanner data. However, 
because the preliminary investigations included a 10-channel 
multispectral scanner, this sensor, after considerable de- 
liberation, was not selected. 



y Color infrared film has an upper spectral limit of sensitivity of 
0.9ijm. Black-and-white infrared films of greater spectral range 
are of low resolution and were deemed of little value to this 
study. 



43 



Multi spectral Scanners 

Multi-channel scanner systems detect and record energy 
in narrow spectral bands simultaneously over a broad range of 
the spectrum, extending from the near ultraviolet through the 
thermal infrared spectral regions. These systems convert the 
detected electromagnetic energy into electrical signals which 
are recorded on magnetic tape. These systems have several 
advantages over film recording devices. The spectral sensing 
and signal dynamic range is much greater than that of film. 
Low energy levels at both the upper and lower spectral limits 
of the visible range do not adequately expose photographic 
film, but this problem is less serious with scanning systems 
because the detected energy is electronically amplified. This 
amplification permits filtering to much narrower spectral 
bands than is possible with camera systems. 

For convenience, multi spectral scanners are grouped 
into two classes: those that detect reflected energy and must 
operate during daylight hours, and those that sense emitted 
energy and can operate day or night (thermal scanners). 

The tape recorded data from multi spectral scanner 
systems are readily adaptable to computer processing. Point 
by point correlations between spectral bands provides the 
possibility of signature analysis and image enhancement. The 
near infrared spectral zone, (.7-3. Oym) contains several 
spectral absorption bands resulting from H2O and CO2 con- 
centrations in the atmosphere. For water and soil moisture 
discrimination a single channel of data positioned adjacent to 
a water absorption at 1.138ym should provide useful informa- 
tion concerning fractures, faults, and landslides or talus 
that concentrate moisture. The Fe"'"^ ferric ion has a strong 
reflectance minima at 0.7ym (Hunt and Salisbury, 1971) that 
can identify iron-rich rocks when ratioed with strong reflec- 
tance spectral bands (Hunt and Salisbury, 1971; Vincent, 
1973). Because of the range of spectral coverage and flex- 
ibility in analysis multispectral scanner data was acquired 
for this study. 

Infrared Scanners 

Monochromatic and polychromatic sensing of reflected 
and emitted infrared energy can significantly complement 
visual photography and video sensors. This enables deline- 
ation of vegetation boundaries, water courses, soil moisture 
differences, rock discontinuities, gross lithologies, and 
other features of interest in site selection. In the spectral 
band from .9-5.5ym the energy radiated by an object ranges 
from predominantly reflected solar energy at the shorter 
wavelengths to predominantly emitted energy at the longer 

44 



wavelengths. Thus, for the sensing of energy of wavelengths 
shorter than about 3.5ym, daylight conditions must prevail. 

Of greater interest is the emitted thermal radiation 
from the terrain in the 8-14ym atmospheric window. Several 
investigators (Lyon, 1964, 1972; Watson, 1971b; Lowman, 1969) 
have demonstrated that soil moisture boundaries, water courses, 
and some lithologic boundaries can be detected by single 
channel analysis of day or night imagery using the differences 
in thermal emission between such features and surrounding 
terrain. 

Silica exhibits emittance minima at approximately 8.1- 
lO.lym and 12.1-13.0ym (Vincent, 1973). Vincent (1972 b and c) 
reported that by ratioing appropriately selected thermal 
spectral bands, the presence of silica could be detected. The 
more acidic the rock, the greater the variation. This pro- 
vides a measure of the silica content of the rock. 

Based on the potential of this sensor to aid in iden- 
tifying dissimilar rock types such as basic dikes in acidic 
rocks, sandstones from non- siliceous rocks, and subtle dif- 
ferences in soil moisture content, a dual -channel thermal 
infrared scanning system was considered to be an important 
sensor for testing during this study. 

Infrared Spectroradiometry 

Infrared spectroradiometry in the 8-14ym region can 
yield mineralogical and chemical composition data for dry 
rocks barren of vegetation by matching the incoming spectrum 
with standard curves in the memory of a computer. 

Lyon (1964) pioneered analysis of multispectral data in 
the 8-1 4ym range and demonstrated the ability to identify 
gross rock types remotely by their characteristic response 
curves. The technique, however, is still experimental and 
suitable sensor systems are not commercially available. 

Microwave Radiometer 

A radiometer consists of a highly sensitive receiver 
and antenna operating in the microwave spectrum between 1 and 
100 gHz; it is designed to detect apparent microwave surface 
temperatures. Microwave brightness depends in a complicated 
way on the physical, chemical, and electrical properties of 
the terrain observed by the radiometer. Thus, it is difficult 
to associate terrain composition and structure with isolated 
measurements of the passive emission. However, multispectral 
radiometric images properly corrected for atmospheric and 
surface roughness effects can provide lithological data. Poor 

45 



resolution and low signal levels and emission differences 
produced by variations in surface roughness and soil moisture 
make this instrument of limited value for tunnel site in- 
vestigation and it, therefore, was not used. 

Scatterometers 

A radar designed to measure the surface scattering 
coefficient is called a scatterometer, and experiments con- 
ducted to define the interaction of electromagnetic waves with 
rough surfaces have been grouped into a field of study called 
scatterometry. Scattering coefficient of the terrain varies 
as a function of incidence angle, aspect angle, frequency, 
polarization, and the surface texture. 

The scattering coefficient varies markedly as the angle 
of incidence of the transmitted wave is varied. It is deter- 
mined primarily by the large scale features of the terrain at 
near-vertical incidence and by the small scale structure at 
near-grazing angle. 

Because the scattering coefficient is a function of the 
transmitted frequency, useful information can be obtained, in 
principle, from a scatterometer that sweeps over a fairly 
narrow frequency band. Presumably a scatterometer that 
obtains a complete frequency response curve over several 
octaves of frequency would permit unique determination of most 
radar targets. In general, the scattering coefficient becomes 
independent of polarization for \/ery rough terrain. However, 
for slightly rough terrain the coefficient might be greater 
for vertically-polarized waves than horizontally-polarized 
waves. Consequently, the coefficient is dependent on the 
frequency, angle of incidence, and the type of terrain. 

The application of scatterometry to tunnel site evalua- 
tion does not appear profitable in that data analysis is 
complex, the results are uncertain, and other sensors and 
ground observations will provide better information. 

Imaging Radar 

Side Looking Airborne Radar (SLAR) is an all weather 
system which can be used day or night for imaging the earth's 
surface when more conventional aerial photographic means are 
not possible. SLAR is an active "system" because it transmits 
its own energy via a directable antenna and it receives that 
portion of the energy that is subsequently reflected by the 
terrain back toward the aircraft. 



46 



Radar uses electromagnetic energy of a much lower 
frequency and much longer wavelengths than either infrared 
scanners or aerial cameras, and thus achieves several advan- 
tages. These advantages include: 1) Radar wavelengths are 
sufficiently long such that they are not reflected or scat- 
tered by the relatively small size water particles in clouds; 
this makes data collection possible in areas of continuous 
cloud cover. 2) The longer radar wavelengths (greater than 
20cm) penetrate vegetation such as scrub brush and forest 
canopies, and, thus, achieve more accurate depiction of 
terrain features. 3) The smaller scale and larger area of 
coverage of radar images permits regional lithologic inter- 
pretation not possible on larger scale aerial photography and 
not discernible on lower resolution small scale satellite 
imagery. 

Radar frequencies range from VHF to the EHF with 
wavelengths ranging from 1 centimeter to over a meter. The 
longer wavelength radars have the greatest potential for 
vegetation penetration and to a more limited extent, soil 
penetration. Ka-band, with the shortest wavelength (1 cm), 
has the greatest potential for mapping vegetation and more 
finely "textured" terrain. 

The phenomona which controls what is recorded on a 
radar image is called radar backscatter. Backscatter is 
affected by a combination of the aspect angle, surface rough- 
ness, and dialectric constant of the terrain. The greater the 
dialectric constant, the greater is the percent of the trans- 
mitted energy reflected. Where the energy is reflected de- 
pends upon the aspect angle and surface roughness of the 
terrain relative to the wavelength of the radar signal. For 
instance, a lake surface or a flat metal roof both have yery 
smooth surfaces and high dialectric constants and thus will 
reflect a high percentage (95%) of the incident radar energy. 
However, because the angle of incidence is always equal to the 
angle of reflection, the backscattered energy reflected toward 
the radar aircraft from the lake will be near zero as all the 
energy will have been reflected away. The energy returned 
from the roof may be zero or larger, depending upon its aspect 
angle. A level plowed field and a level road have similar 
dialectric constants and aspect angles, but the plowed field 
will return much more energy because of its greater surface 
roughness. 

Multi spectral radar using two bands such as L-X Band is 
useful for analysis of both gross geomorphologic features and 
fine-textured vegetation. A given surface may appear smooth 
to an L-Band (30 cm) wavelength, but rough to a Ku-Band (3 cm) 
wavelength and discrimination between surfaces is therefore 
possible. 

47 



Polarization of the transmitted wave and acceptance 
polarization of the receiving equipment is another means of 
classifying terrain properties. Some radar systems can 
transmit and receive in both horizontal polarization (HH) and 
vertical polarization (VV), while still other systems can 
cross polarize (HV or VH) and do any combination of the above 
in two bands. 

Shadowing is a normal and unavoidable phenomenon in 
radar mapping which occurs because the radar transmitter 
illuminates the terrain at a low angle. Thus, for a given 
altitude and ground range, if an object such as a mountain 
blocks the signal, no radar data will be obtained from targets 
behind the mountain. This "shadow" area will be imaged as 
black on the radar positive prints and its effect is a shadow 
enhancement of topographic and geologic features. 

Because of its sensitivity to aspect angle and surface 
roughness, radar imagery provides an excellent synoptic pic- 
ture for regional geological structural evaluation of an area, 
particularly if the area possesses moderate to low relief. 
The imagery is small scale, even with enlargement. However, 
this can be an asset because it eliminates distracting detail 
which might otherwise obscure useful geologic structural 
information. SLAR surveys require sophisticated aircraft and 
instrumentation, and commercial surveys are expensive. SLAR 
imagery flown by the U.S. Air Force was available for both 
test sites at a nominal cost. 

Airborne Geophysical Surveys 

Airborne geophysical contractors provide routine surveys 
that measure variations in three basic properties of rocks 
near the surface. 

1. Variations in the magnetic field strength caused by 
the geometry and differences in content of magnetic 
minerals in the rocks. 

2. Variations in the induced electromagnetic field 
strength caused by the geometry and primarily by 
differences in conductivity of near surface rocks. 

3. Variations in the intensity spectra of gamma radia- 
tion caused by differences in the content of radio- 
active elements in the surface rocks. 

The routine surveys conducted by these contractors use 
instrument systems that are designed with specific raw mate- 
rial exploration programs in mind. These systems have much 
higher capital costs and much higher hourly survey costs than 

48 



equivalent ground survey systems. The only justification for 
these higher costs is the much lower unit cost in large area 
surveys. Cost effectiveness comes generally from the mapping 
of relatively large areas on more of a reconnaissance basis 
than ground surveys. Thus, there is a great reduction in but 
not an elimination of the area to be covered by ground surveys. 

Airborne Electromagnetic Systems 

Airborne electromagnetic (AEM) systems are designed to 
measure variations in the conductivity of the ground beneath 
the aircraft. Many major fracture zones are substantially 
more conductive than the rocks that contain them when water, 
graphite, or metal sulfides are present. AEM systems operate 
at frequencies from about 300 Hz to 8,000 Hz. The lower 
frequencies explore depths down to perhaps as much as 650 feet 
(200m) beneath the earth's surface. The systems basically 
consist of two coils; a transmitter, and a receiver coil. A 
generator loads the transmitting coil at the frequency desired 
and the secondary fields at the receiver are measured and 
referenced as to phase. In some systems more than one receiv- 
ing coil is used and in some more than one frequency is used. 
In general, the lower the frequency the greater the depth of 
penetration, but the less discrimination of conductivity and 
resolution of anomalies in space. Lower frequencies also 
require heavier power generators and larger aircraft. 

There are a great many AEM systems available from many 
contractors, and almost all surveys are flown by the contractors 
because most systems are wery difficult to install and operate. 

The quantity measured by EM systems is the rock con- 
ductivity multiplied by some significant dimension of the 
conductor (for veins, fault zones and tabular bodies, it is 
the conductivity multiplied by the thickness of that body). 
The frequency range is chosen for good conductivity discrim- 
ination among the better conductors. Some of these systems 
are capable of determining the orientation as well as the 
location of conductive zones, thus making it possible to 
determine the strike and dip of major shear zones that contain 
water or for some other reason are good conductors. Such 
systems have the potential of providing valuable engineering 
data, particularly in igneous rock sites. It is also one of 
the few airborne sensors with a capability of sensing beneath 
the earth's surface. Based on these factors, it was recom- 
mended for testing on one tunnel site. 



49 



Airborne Magnetometer 

Designed during World War II to detect submarines, the 
airborne magnetometer measures either variations in the 
earth's magnetic field or the total magnetic field with great 
precision. The variations in the earth's magnetic field are 
due primarily to variations in the concentration of two 
minerals: (1) magnetite, a very coninon mineral whose concen- 
tration varies systematically and predictably with rock type; 
and (2) pyrrhotite, a rather uncommon mineral often associated 
with massive copper-zinc sulfide ore bodies and sulfide-iron 
formations. 

Aeromagnetic surveys are generally included when other 
airborne geophysical surveys are flown because the additional 
cost is small and the data are a useful aid in interpreting 
other sensor data. For these reasons, a magnetometer was 
included in the AEM survey package. 



4.3.3 Satellite Remote Sensors 

The LANDSAT-1 satellite can acquire multi spectral 
imagery every 18 days, atmospheric conditions permitting, of 
any specific point on the earth's surface between Lat. 81 °N 
and Lat. 81 °S latitude. In January 1975, LANDSAT-2 was 
launched and was placed in an orbit such that it is now 
possible to obtain repetitive coverage every nine days, or 
less at higher latitudes. Four spectral bands of data ranging 
from .B-l.lym are obtained simultaneously, permitting the 
composite reconstruction of false color images. Although the 
resolution of the system is approximately 250 feet (80 meters) 
the imagery has proven to be an excellent source of regional 
geologic data. This is particularly true for mapping linea- 
ments and fractures. Analysis of LANDSAT data in conjunction 
with high, medium, and low altitude aerial photography has 
shown that many obvious lineaments on LANDSAT imagery are not 
identifiable on the larger scale photography. This indicates 
that the satellite data is a source of valuable and unique 
geologic information. 

Imagery and photography from the Skylab satellite has 
better spatial resolution than that from the LANDSAT system, 
but only limited amounts of data were obtained because the 
film and tapes were hand carried back to earth. 

The acquisition of LANDSAT and Skylab imagery is 
recommended for each site to obtain the regional geologic 
"picture" of the tunnel site. Selected LANDSAT imagery 



50 



obtained during the various seasons of the year should be used 
because experience has demonstrated that some geologic infor- 
mation is emphasized by certain seasonal changes. 



4.3.4 Other Remote Sensors 

There are several remote sensing instruments, par- 
ticularly those that operate in the radio frequency range, 
which show some potential of providing useful data for tunnel 
site studies; however, they are either unavailable commer- 
cially or are in the development state. These include imaging 
microwave radiometers, long wavelength monocycle radar, and 
multi frequency SLAR systems. Still others, while available 
commercially, are judged to be of little value to the program, 
either because low value or redundancy of the data acquired, 
or too high a cost of data acquisition. In this category are 
included the scatterometer and the passive microwave radiom- 
eters. Some systems, such as the airborne gravity meter, have 
such gross resolution that it is of little value for tunnel 
site studies. 



4.3.5 Sensor Complement Selected 

After consideration of the potential contribution of 
the various remote sensors, their commercial availability and 
comparative cost, the following suite of remote sensors were 
selected for use in this investigation and evaluation: 

a. LANDSAT imagery 

b. Skylab photography 

c. Radar imagery 

d. Low-sun-angle photography (LSAP) 

e. Medium and large scale aerial photography 

1. natural color 

2. color infrared 

3. panchromatic black-and-white 

f. Multi spectral scanner imagery (visible-near-visible) 

g. Dual-channel thermal infrared imagery 
h. AEM 

i. Magnetometer 



51 



5.0 SITES SELECTED 

5. 1 Carl in Canyon Tunnel Site 

5.1.1 Project Area Description 

The Carl in Canyon was produced by the Humboldt River 
where it cuts through the Adobe Pinon Range (Figure 2). This 
northerly trending mountain is one of a series of fault block 
mountain ranges characteristic of much of Nevada. The range 
is narrow and where intersected by the Humboldt River it is 
approximately four miles (6.4 km) wide. 

The name, Carl in Canyon, is restricted to that portion 
of the river valley which forms a narrow, horseshoe-shaped 
bend nearly a mile (1.6 km) long and a quarter (0.4 km) wide. 
The canyon appears to be a superimposed stream meander, but 
fractures and bedrock structure have influenced the final 
shape of the channel. 

The elevation at riverbed level is approximately 5,000 
feet (1,500 m) , but rises abruptly to over 5,500 feet (1,675 m) 
within a horizontal distance of 600 feet (180 m). More 
gently sloping terrain extends to an elevation of over 6,600 
feet (1,830 m) at Buckskin Mountain four miles to the south. 

The curvature of Carl in Canyon is too small to meet 
interstate highway curve specifications. It was, therefore, 
necessary to construct a 1,500 foot (457 m) tunnel through the 
500 foot (152 m) high ridge in the canyon. This north-south 
trending ridge is largely covered with talus and soil on the 
western side. The eastern side exhibits steeper slopes, 
numerous bedrock exposures and scattered accumulations of thin 
soil. 



5.1.2 Geologic Setting 

The Carl in Canyon tunnel site is located in north- 
eastern Nevada in an area of the western United States known 
as the Basin and Range physiographic province. This is an 
area of long, narrow, fault-block mountains separated by broad 
closed basins that are partially filled with alluvial deposits. 

The bedrock of the area is mainly marine sedimentary 
rocks formed in shallow and deep seas that covered the area 
during the middle and late Paleozoic era. These deposits were 
laid down in tabular units which are relatively thin but 
laterally extensive. Uplift and erosion interrupted deposi- 
tion of these sedimentary units at least once in the Carl in 

52 




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53 



Canyon area, and destroyed the parallelism of successive units 
and created an angular unconformity. 

Non-marine conditions have persisted in the area since 
the late Paleozoic era. Tectonic forces have created major 
faults, minor folding, and some volcanic activity. The 
present-day ranges are the result of movements along mainly 
north-south faults. The total movement along these faults 
appears to be on the order of 10,000 feet (3,048 m). The 
present maximum relief of 3,000 feet (914 m) to 4,000 feet 
(1,219 m) is the result of continued erosion of the uplifted 
ranges and partial filling of the intervening basins. 

The climate of the area is arid but a more temperate 
climate has prevailed in the past. There is evidence that the 
area had a humid climate with forests and extensive lakes 
during the Pleistocene epoch. This more moderate climate 
accounts for the gently rounded upland surfaces and the pres- 
ence of moderately thick soil zones at some locations. 

The bedrock of the Carl in Canyon tunnel site is com- 
prised of two formations: the Diamond Peak formation composed 
of conglomerates, sandstones, and some shale partings; and the 
Strathearn formation composed primarily of limestone. Both 
formations are well exposed on the spur at the tunnel and 
along the canyon walls upstream and downstream of the site. 
At the base of the canyon walls and along the river the bed- 
rock is covered by deposits of colluvium and alluvium. 

The Diamond Peak formation of Pennsylvanian-Mississippian 
age is the lower or older formation. It is primarily exposed 
on the west side of the spur and on the west end of the can- 
yon. It is composed of 3-5 foot (1-1.5 m) beds of conglomerate 
and sandstone with interbeds of shale and siltstone which 
range in thickness from a fraction of an inch to several feet. 
The thick-bedded conglomerate and sandstone are well cemented 
by quartz, chalcedony, and iron oxide, and contain a widely- 
spaced pattern of joints. The thinner shale and siltstone 
interbeds are closely jointed in outcrop. The better cemented 
zones in the rock mass form conspicuous tabular units along 
the walls of the valley while less well cemented zones are 
found in narrow grooves and gullies on the outcrops. 

The Strathearn formation is a Permian-Pennsylvanian age 
deposit of hard, medium- to- thick-bedded limestone with thin 
interbeds of shale. The Strathearn formation is exposed on 
top of the spur, on the east side of the spur, and on the 
walls of the eastern portion of the canyon. Most limestone 
outcrops display several sets of closely-spaced joints of 
different orientations. These joints, bedding planes, and 



54 



shale interbeds limit the average size of the intact limestone 
blocks to less than one foot (.3m) in most exposures. The 
rock in natural exposures, however, appears relatively stable 
because the small rock blocks have an irregular shape and a 
high degree of interlock. 

The bedding in the underlying Diamond Peak formation 
has a strike of north 10-20 degrees west and a dip of 85 
degrees east. The bedding in the overlying Strathearn for- 
mation has a strike of north 15-40 degrees west and a dip of 
60-80 degrees east. The contact between the two formations 
represents a hiatus in deposition of many millions of years. 
During this period the Diamond Peak formation was uplifted 
above sea level, eroded, and submerged. Deposition of the 
Strathearn formation then occurred during this submergence. 
This contact is termed an angular unconformity because of the 
angle between the bedding above and below the contact and the 
identifiable break in deposition between the formations. 

Neither of the two major faults identified at the 
Carl in Canyon Tunnel area intersect the tunnel alignment. A 
reverse fault crosses the northeast portion of the spur coming 
to within 100 feet (30 m) of the east tunnel portal. The 
total vertical displacement on this fault is approximately 300 
feet (90 m) , but it is sufficient to expose the Diamond Peak 
rocks within the outcrop belt of the Strathearn formation. A 
second fault zone has been identified south of the west portal. 
The nature of the movement along this fault has not been 
defined from surface mapping but it does not intercept the 
tunnel. Minor faulting along the bedding has been noted in 
both formations. 

Unconsolidated deposits of sand, gravel, and boulders 
are found at the west portal. These deposits include terrace 
remnants of the Humbolt River alluvial deposits and colluvium 
which has accumulated at the base of the spur. 



5.1.3 Site Investigations 

Most of the previous geologic investigations of the 
area are limited to regional bedrock studies to define general 
stratigraphic and structural relationships and to identify ore 
deposits. The reports of these investigations provide in- 
formation about rock type and the geologic history of the 
area, but contain no specific information about the behavior 
of the rock in an underground excavation. Dott (1955) re- 
ported on the Carl in Canyon area and named the conglomerate 
series the Tonka formation, although asserting it probably 
correlated with the Diamond Peak formation named in 1883 at a 

55 



site 90 miles (144 km) away. Smith and Ketner (1975) believe 
the relationship between the two sites are adequately con- 
firmed and have used the name Diamond Peak in the Carl in 
Canyon. A portion of their map is reproduced as Figure 19, 
Section 7.4.1 . 



5.1.4 Ground Conditions 

The investigations indicated that the rock at the 
Carl in Canyon site is generally competent for the proposed 
tunnel excavation. Both tunnels could be excavated full face 
with the possibility of some difficulty in the more fractured 
parts of the Strathearn and at the unconformity. Fractured 
zones in the Strathearn near the east portal where the rock is 
in relatively close proximity to the reverse fault would 
probably represent the greatest difficulty in tunnel excava- 
tion. The angular unconformity, anticipated 800 to 1,000 feet 
(244 to 305 m) from the east portal, should be a feature of 
minor importance during tunnel excavation. 

The bedrock is expected to be essentially dry through- 
out the length of both bores. Water inflows encountered 
during this work should be small and of relatively short 
duration because of the limited drainage area on the spur, 
limited rainfall in the area and pre-drainage of the ground by 
the adjacent railroad tunnels. There was no evidence of other 
geologic problems which might affect the progress of the 
excavation. 

The investigation did indicate the presence of thick 
deposits of unconsolidated materials at both portals. Ex- 
cavation of the portal cuts could involve the removal of a 
greater than anticipated volume of soil and rock in order to 
establish suitable foundation conditions for the portal 
structures and acceptable rock conditions to start the tunnel. 



5.2 East River Mountain Tunnel Site 

5.2.1 Project Area Description 

East River Mountain Tunnel is a twin-bore tunnel for 
Interstate Route 77 located approximately five miles east of 
Bluefield, West Virginia. The tunnel provides a low-level 
crossing through the 1,400 foot (427 m) high East River 
Mountain which separates Bland County, Virginia on the south 
from Mercer County, West Virginia on the north. Figure 3 is 
an aerial oblique view of the mountain and north portal of the 
tunnel. 

56 




Figure 3 - South looking oblique airphoto showing the north portal of the East River Mountain tunnel 
in the foreground. The sharp crest of the mountain, formed by the Tuscarora sandstone, is prominent 
in the upper left portion of the image. The haze apparent in this picture is characteristic of the area. 



57 



5.2.2 Geologic Setting 

East River Mountain is a long Appalachian Mountain 
ridge located on the western side of a 40-60 mile (64-97 km) 
wide belt of parallel ridges and valleys which extends from 
northern Georgia to eastern Pennsylvania. This topography is 
the product of long periods of erosion on folded sedimentary 
rocks. The ridges are underlain by rock which is resistant to 
erosion, while the valleys are underlain by less resistant 
rock. Faulting is present on both a regional and local scale. 
The geology is dominated by folded and faulted structure, 
while the topography is dominated by erosion landforms. 

The bedrock is mainly Paleozoic-age sedimentary rock 
including sandstone, quartzite, shale, and limestone. Region- 
al studies show that the sedimentary sequence has a total 
thickness of 30,000 feet (9,144 m). Individual units or 
formations are generally tabular in form with a thickness 
commonly ranging from 10-1,000 feet (3-300 m) , and lateral 
dimensions ranging from several tens of miles to several 
hundred miles. These rocks were formed by deposition in a 
shallow sea which covered the area between the Cambrian and 
the Pennsylvanian periods. The formations were laid down in 
approximately a horizontal orientation and the contacts be- 
tween adjacent units were essentially parallel. Folding 
arched the strata into anticlines and synclines. This folding 
was accompanied by uniform regional deformation which produced 
extensive reverse and thrust faulting. This faulting resulted 
in the repetition of the stratigraphic section and is express- 
ed topographically as a series of ridges which are capped by 
the resistant Tuscarora sandstone (see radar imagery. Figure 
10, Section 7.2.2). The ridges in the general area of East 
River Mountain are tilted blocks with little cross-faulting 
evident. 

The main trend of the ridge and valley belt is east- 
northeast. The location of individual ridges and valleys 
depends upon the local bedrock structure, the relative re- 
sistance of the formations to erosion, and the depth of 
erosion within that area. 

The master streams of the area flow across the ridge 
and valley belt toward the Atlantic ocean passing through the 
ridges in major water gaps. The secondary streams are found 
in the valleys parallel to the ridges. Drainage on the ridges 
is generally restricted to small tributaries of these secon- 
dary streams. 



58 



East River Mountain is topographically asymmetrical with 
a relatively gentle south-facing slope {approximately 20°) and 
a relatively steep north-facing slope (approximately 30°). 
The ridge is underlain by a series of strata including sand- 
stone, shale, and limestone, which have a strike of north 65 
degrees east and a dip of approximately 25-40 degrees south. 

The ridge owes its existence and form to the Tuscarora 
sandstone cap rock which controls the topography on the upper 
two-thirds of the south slope. The topography of the lower 
part of the south slope is controlled by the less competent 
Rosehill shale and resistant Keefer sandstone and Rocky Gap 
sandstone that overlie the Tuscarora formation. The upper 
part of the north slope is a sheer cliff face which exposes 
nearly the full thickness of the Tuscarora formation. Less 
steep slopes are formed in the underlying Juniata shale, 
Martinsburg shaly-limestone, and Eggleston, Moccasin, and 
Gratton limestones. The limestones form a hummocky topography 
at the base of the slope and the floor of the adjoining 
valley. This area exhibits limited surface drainage and 
numerous sinkholes indicating the presence of extensive sub- 
surface solution openings. 

With the exception of the Tuscarora formation, there 
are few natural outcrops of the rocks at East River Mountain. 
The Tuscarora formation is well exposed in the ridge crest on 
both the northern and southern slopes. Outcrops of the 
Rosehill, Keefer, Rocky Gap, and Huntersville formations are 
naturally exposed in only a few places on the southern slope. 
The Keefer sandstone is exposed in the roadcut along State 
Highway 52; the Rosehill is also exposed in a road cut and 
slide areas along Highway 52. The Juniata, Martinsburg, and 
Moccasin formations do not crop out on the northern slope in 
the immediate area of the tunnel site because of residual 
soils and colluvial cover. 

The soil cover on the upper part of the ridge is gen- 
erally thin and discontinuous. The lower ridge, particularly 
on the south slope, is mantled by extensive, but thin residual 
soil and colluvial deposits. The deposits on the lower part 
of the north slope are relatively thin and composed of col- 
luvial clay and sand, and residual clays formed on the lime- 
stones. 

The St. Clair thrust fault is present approximately 
2,000 feet (610 m) north of the north portal. This fault does 
not cut the tunnel area, although the limestones at tunnel 
level may be displaced on a small scale by related faults. 



59 



5.2.3 Site Investigations 

Previous local and regional studies document the bed- 
rock geology of East River Mountain. The U.S. Geological 
Survey mapped the area in the late 1800's and published the 
results of this study in the Pocahontas Folio dated 1896. 
Published regional studies of the Devonian age formations and 
the Tuscarora and Juniata formations include observations made 
on East River Mountain. 



5.2.4 Ground Conditions j 

i 
The Keefer and Tuscarora sandstones appear to be com- 
petent and, therefore, will provide good ground conditions. j 
The Rocky Gap formation is incompetent because of clay or ' 
shale interbeds and noncemented sands. The Juniata and ; 

Martinsburg shale, shaly limestone, and siltstones, although 
softer than the Tuscarora and Keefer sandstones, are relatively 
competent. The shales and siltstones of the Rose Hill forma- ' 
tion appear less competent because of the presence of inter- I 
bedded soft shale layers. The Moccasin, Witten, and Gratton i 
limestones are hard and relatively competent except in the 
vicinity of solution openings. 

Artesian groundwater conditions may exist in the soil 
deposits and the bedrock near the south portal. The incom- 
petance of the rock formations, the residual soil, and col- 
luvial deposits on the south slope require excavation to the 
competent Keefer formation to start tunneling. 



60 



6.0 SITE INVESTIGATIONS 

Field activities at each site were divided into three phases 
pre-flight, flight support, and data verification. 



6.1 Pre-Flight 

After tentative selection of the test sites, field parties 
visited each site to make a final decision on the suitability of 
the sites for the purposes of the investigation. With the 
acceptance of the sites, specific plans were made for the conduct 
of the remote sensor overflights and the logistic support require- 
ments for these activities. In addition, during this visit to 
each site, the structural and stratigraphic geology in the vicinity 
of the tunnel site was inspected. Strike and dip measurements 
of joints and bedding planes were recorded and rock samples were 
collected for future study. Traverses were made above the tunnel 
site to identify lithologic contacts, faults, discontinuities, 
and other structural features, such as sink holes, which are 
present at the eastern test site. Qualitative analysis of rock 
properties were made, including hardness, resistance to erosion, 
conformable relationships, uniformity of rock composition, presence 
and density of fracturing and condition of fracture surfaces. 
The results of these early field investigations are discussed in 
Section 5.2. 



6.2 Flight Support 

A second trip to each site was made to support the flying 
missions, especially for the collection of night-time thermal 
imagery. Temperature measurements were made prior to the over- 
flight on various target materials to determine when the effects 
of the daytime solar heating had dissipated. At both test sites, 
it was determined that the insolation effects were minimal by 
11 p.m. and useful thermal imagery could be acquired after that 
time. At the western site, pre-dawn thermal imagery was also 
acquired. It was not possible to acquire pre-dawn thermal imagery 
at the eastern site due to the development of ground fog during 
the early morning hours. 

While the thermal scanner was being flown, temperature 
measurements of various target materials on the ground were again 
recorded to supplement the black-body temperature reference data 
from the scanner. These temperature measurements were useful 



61 



later during digital image processing when attempts were made to 
isolate specific targets within a narrow thermal range. To aid 
in data analysis, additional measurements were made including air 
temperature, relative humidity, wind speed, and wind direction. 
The flight lines for the night-time thermal survey were marked by 
handheld lights at predetermined locations. 

At the eastern test site the survey was performed on 
1 April 1975. Conditions for conducting a thermal survey were 
less than ideal because over two inches of rainfall had been 
recorded during the 72 hour period preceding the overflight. The 
mission could not, however, be postponed because of flight 
scheduling problems. Furthermore, spring emergence of leaves 
soon would have obscured the ground surface. 

Tables 1 and 2 are summaries of pertinent data for imagery 
acquired for each site. 



6.3 Data Analysis Verification 



The third phase of the field activities involved return 
trips to each test site to verify the interpretations derived 
from the imagery and to test the hypothesis of the three dimen- 
sional geologic model. Various features of geological interest 
had been located and isolated on aerial photography, thermal and 
multispectral imagery and tentative identifications of different 
lithogolies had been made on the multispectral imagery. These 
features were investigated on the ground and the results of the 
investigation supported most interpretations. There were some 
discrepancies, however, on the multispectral ratio images between 
the expected response and the actual response of the sensor. A 
detailed discussion of these anomalies appears in Section 7.8. 

At the Carl in Canyon Site, both ratioed multispectral and 
thermal data failed to reliably discriminate the Diamond Peak 
conglomerate and the Strathearn limestone. To better understand 
this problem, a portable spectroradiometer (ISCO Model SR) was 
taken to the site to make comparative measurements. The results 
of these measurements, given in Appendix E, indicated a maximum 
difference of less than 3% in relative reflectance between the 
weathered surfaces of the two formations in any portion of the 
spectrum measured. 

Supplemental field examination is needed in most remote 
sensing surveys to verify the analysis of the data. Once the 
spectral characteristics of specific rock types in an area are 
known, the rock type can then be generally identified throughout 
the area. However, the effects of the local environment must be 

62 



Table I Summary of Pertinent Data for Imagery Acquired of the East River Mountain 
Virginia - West Virginia Tunnel Site 



TYPE 
IMAGERY 


IMAGE ID 


DATE 


TIME 


ALT(AMT) 


SCALE 


IMAGE FORMAT 


LANDSAT-1 


1280-15320 


73-4-29 


9:30 am EST 


496 n.mi. 
(920 km) 


1:3,369,000 

1:1,000,000 
1:1,000,000 


70mm pos & neg 

transp . 
7" X 7" b&w prints 
Color composite 

print 


LANDSAT-1 


1209-15374 


73-2-17 


9:30 am EST 


496 n.mi. 
(920 km) 


1:3,369,000 


Color composite 


SKYLAB 
S-190A&B 


RL 46-FRM22 


73-9-16 
73-9-16 


3:50 pm EST 
3:50 pm EST 


235 n.mi. 
(435 km) 


1:2,850,000 
1:950,000 


b&w 70mm neg. 
Color composite 
transp. 


SIDE 
LOOKING 
RADAR (SLAR) 


NG665-079 

PNOl 


62-3-16 






1:600,000 


b&w print and 
pos. transp. 


LOW SUN 
ANGLE 
PHOTO- 
GRAPHY 
(LSAP) 




74-4-5 
74-4-7 


6:37 pm EST 
7:35 am EST 


20,000' 

AMT 
20,000' 

AMT 


1:40,000 
1:40,000 


9" X 9" b&w prints 


COLOR 

PHOTOGRAPHY 


1236-46 
1219-34 


75-4-27 


1:20 pm EST 
12:45 pm EST 


18,000' 
6,000' 


1:36,000 
1:12,000 


9" X 9" color 
prints 


PANCHRO- 

MATRIC 

PHOTOGRAPHY 


555-95-57 
555-114-116 






6,000' 


1:12,000 


9" X 9" b&w 
prints 


COLOR IR 
PHOTOGRAPHY 




75-4-6 
75-4-27 


12:30 pm EST 
1:20 pm EST 


15,000' 
3,000' 


1:30,000 
1:16,000 


9" X 9" pos. trans. 


THERMAL 
INFRARED 
& MULTI- 
SPECTRAL 
SCANNER 


See 

Appendix F 


75-4-1 


4:30 pm EST 
11:00 pm EST 
1:45 pm EST 


6,000' 
2,500' 
6,000' 
2,500' 


1:24,000 
1:10,000 
1:24,000 
1:10,000 


l/2m, 7-track 
mag. tape, 
70mm neg. b&w 
prints 


MAGNE- 
TOMETER 
AIRBORNE 

EM 




75-10-8 

to 
75-10-22 




180' 
130" 




line charts 
line charts 



63 



Table 2 Summary of Pertinent Data for Imagery acquired of the Carlin Canyon Nevada Tunnel Site 



TYPE 
IMAGERY 



IMAGE ID 



DATE 



TIME 



ALT(AMT) 



SCALE 



IMAGE FORMAT 



LANDSAT-l 1396-17590 73-8-23 10:00 am MST 496 n.mi. 1:3,369,000 

(920 km) 



70nim neg. & pos. 
trans, color print 



SKYLAB 
S-190A 



85-003 



73-8-12 



235 n.mi. 
7:44 am MST (435 km) 



1:2,850,000 70mm negs. 



SIDE FN3123-J 73-5-3 

LOOKING PN 15 

AIRBORNE FN 1155-G 71-6-4 

RADAR PN 01 

(SLAR) 



1:400,000 
1:200,000 



b&w print film neg. 



LOW SUN 04 
ANGLE PHOTO- 
GRAPHY 06-08 
(LSAP) 



06 74-10-18 8:15 am MST 18,000' 1:38,600 b&w print 
74-10-18 5:00 pm MST 18,000' 1:38,600 b&w print 



PANCHROMATIC 4-6 
PHOTOGRAPHY 1-6 



74-7-25 10:20 am MST 18,000' 1:39,000 
74-5-9 10:50 am MST 3,000' 1:6,000 



9" X 9" b&w print 
9" X 9" b&w print 



COLOR 



23-25 74-10-18 11:05 am MST 15,000 1:30,000 
16 - 22 74-10-18 3,000 1:6,000 



9" X 9" color print 
9" X 9" color print 



COLOR IR 



Not num- 
bered 

10-15 



74-10-18 12:00 pm MST 15,000' 1:30,000 
12:15 pm MST 3,000' 1:6,000 



9" X 9" pos. transp. 
9" X 9" pos. transp. 



THERMAL 
INFRARED 
Aim MULTI- 
SPECTRAL 
SCANNER 



See 74-10-17 11:30 pm MST 6,000' 1:24,000 
Appendix F 74-10-19 6:40 am MST 3,500' 1:14,000 
74-10-18 10:45 am MST 



1/2 inch, 7-track 
mag. tape, 70mm 
neg. b&w print 



64 



understood as they can produce anomalous results. At East River 
mountain, for example, ratioed multispectral and thermal data 
showed only few characteristic iron responses from the iron-rich 
Rose Hill formation and a silica response was absent from the 
areas where the Tuscarora Sandstone formation is located. A 
field check revealed that a near 100% lichen cover on all naturally 
occurring rock outcrops was the reason for the failure of the data 
processing to identify and differentiate between the Tuscarora 
and Rose Hill formations. This illustrates that, for proper 
mission planning, a knowledge not only of the sensor capability, 
but of the environmental conditions at a test site, are essential. 



65 



7.0 DATA ANALYSIS 

The data from the various remote sensors were analyzed v/ith two 
levels of application in mind; (a) to evaluate the regional geology 
and identify a potential site for tunnel construction; and (b) to 
acquire as much information as possible about a specific site once the 
location of the tunnel was established. 

A regional analysis of the geology is more rapidly and often more 
effectively made with the use of small scale imagery, however, much of 
the same imagery also should be applied to the study of specific 
sites. In any investigation, it is most logical to proceed from the 
small scale imagery for establishing a regional geological setting to 
the large scale data for detailed site specific information. This 
approach also conforms to practical constraints in that the majority 
of investigations start with the examination of existing data, which 
in most instances will be small scale published geologic maps or 
satellite and radar imagery. 

The following discussion of the interpretation and analysis of 
the various types of imagery is presented with the assumption that the 
reader has some knowledge of geological principles, but is not necessar- 
ily familiar with remote sensing. Observations are made as to what is 
seen on the imagery and the conclusions made. Conclusions are drawn 
from the independent analysis of each type of imagery; however, as in 
an operational situation, some conclusions are tentative and subject 
to later modification when higher resolution imagery is examined or 
data from other sources are included. To give the reader a better 
appreciation of what information is present in the imagery, an annotated 
image is included with an unannotated image where it was deemed appro- 
priate. 



7.1 Satellite Imagery 

Numerous geological investigations conducted since 1972 have 
demonstrated that the analysis of small-scale satellite imagery 
may produce significant new geological information. This informa- 
tion is not necessarily better than other information, but it is 
unique. This imagery has revealed that much of the earth's 
surface is marked by major linear features (lineaments). Subsequent 
ground investigations have demonstrated with high probability 
that many of these features are large fracture or fault zones 
(Woodruff et al . , 1974, Kowalik and Gold, 1975). 

Imagery from LANDSAT (formerly ERTS) and Sky lab satellites 
was examined for both test sites to establish the regional tectonic 
setting and to determine if major faulting in the immediate areas 
of the sites could be identified (a description of the LANDSAT 
and Skylab systems appears in Appendix I). 

66 



7.1.1 Carl in Canyon 

A 1:500,000 scale, color composite LANDSAT image of 
the Carl in Canyon area was obtained from EROS Data Center 
(see Appendix I) for evaluation. An examination of the full 
LANDSAT image, which covers over 10,000 sq. miles (25,900 
sq. km.), reveals evidence of major tectonic activity throughout 
the region with some basin and range faults extending completely 
across the image for a distance of over 100 miles (160 km.). 
Figure 4 is a portion of this image. The Carl in Canyon site 
(Figure 4B, Point E) appears to be situated at a flexure 
point or zone of change in the structural trend. To the 
south of the Carl in Canyon about 10-20 miles (16-32 km.), in 
the vicinity of Point A, the structural trend is predominantly 
N 10°-15° W. Immediately north of the Humboldt River, 
Point B, the trend is about N 20°-30° E. Such a flexure 
associated with basin and range type faulting can only add 
complexity to the structure in the Carl in Canyon area. The 
trend of the Humboldt River in the general area of the site. 
Points C and D, is southwest. However, where the river 
crosses the mountain range of the Carl in Canyon site. Point 
E, the trend changes to a northwesterly direction. The 
alignment of the river channel on both sides of the horseshoe- 
shaped Carl in Canyon suggests structural control. To the 
immediate south of Carl in Canyon, at points F and G, two 
major linear features are visible on the LANDSAT imagery. 
These features are quite prominent and seem to terminate at 
the Humboldt River on each side of the tunnel site. This is 
further evidence that considerable faulting has occurred in 
the Carl in Canyon area. 

S-190A black-and-white and color Skylab photography 
were available for the Carl in Canyon area. Portions of 
these 70mm images were enlarged to a scale of 1:250,000 for 
analysis. The color image exhibited less resolution than 
the black-and-white panchromatic film, and the monotone 
color of the area did not contribute to the analysis. 
Consequently, this photography was not used for final analysis. 

The black-and-white S-190A photography of the red 
portion of the spectrum. Figures 5A and B, shows greater 
detail of the area than does the LANDSAT image. This photograph 
confirms the structural complexity of the area and shows 
more clearly the two major northeasterly trending lineaments 
(Points A and B) bracketing the Carl in Canyon area (Point 
C). This further suggests that they are of structural 
significance. The Skylab photograph does not provide evidence 
that the northwesterly trend of the Humboldt River is structurally 
controlled, but does add detail to the change in the structural 
trend in the area. Numerous anomalous drainage patterns in 

67 



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69 



the immediate area of the tunnel site indicate control by 
faulting, fracturing, or bedding planes. 

In summary, the LANDSAT and Skylab imagery indicates 
considerable structural complexity in the Carl in Canyon 
area. The test site appears bracketed by two major faults, 
and a cross-fault controlling the northwesterly trend of the 
Humboldt River may exist. Other lineaments in proximity to 
the tunnel site may represent faults or fracture zones. 



7.1.2 East River Mountain 

For geological analysis, LANDSAT imagery acquired in 
the winter months, when the solar elevation is low, provides 
a shadow enhancement of the terrain features not attainable 
at other seasons. Another advantage of winter imagery is 
that a thin snow cover can also enhance terrain features 
(Wobber, et al . , 1973). A third advantage is that maximum 
visibility of the ground in the heavily forested, eastern 
test site area occurs in mid-to-late winter when the trees 
have lost their leaves and the leaf blanket has compacted. 
LANDSAT imagery of the Bluefield, West Virginia area has both 
a low solar elevation and a thin layer of snow. 

The color composite LANDSAT image of the area. Figure 
6A, clearly shows the highly dissected Cumberland Plateau at 
the upper edge of the image and the folded and faulted Appala- 
chian valley-and-ridge structure in the lower two-thirds of 
the image. This image and Figure 6B were enlarged to a scale 
of approximately 1:200,000 for direct comparison with the 
radar image shown in Figure 10. Figure 6B is a black-and- 
white print of the red spectral band (.6-.7ym) used in the 
preparation of the color composite image. The resolution on 
this image is somewhat greater than for the composite image 
and contains considerable information on the regional geology. 
The color composite, perhaps because of the excessive snow 
cover, provides only limited information beyond that of the 
black-and-white print. On these images both the East River 
Mountain and the Big Walker Tunnel Sites are visible at A and 
B, respectively. These two ridges and the intervening ridges 
appear identical on the imagery, and it seems reasonable to 
assume that folding and faulting has caused numerous repeti- 
tions of the stratigraphic section. Although deformation has 
tilted the ridges so that the beds dip moderately to the 
south, the ridges appear to be reasonably continuous with 
little or no cross-faulting parallel to the tunnels. Conse- 
quently, at this scale, there appears to be no major fractures 
to complicate the construction of tunnels in these two areas. 

70 











Figure 6A -This 1:200,000 scale color composite of LANDSAT image (no. 1209-15374) was acquired on February 17, 1973, 
when the solar elevation was about 33 . This low illumination angle emphasized the topography which reflects the geological 
structure of the area. This was further enhanced by a thin snow cover. See Figure 6B for the geological interpretation. 



71 




^'&^*if- 



•.???; 



















Figure 6B - This red spectral band LANDSAT image used in creating Figure 6A shows excellent detail of the geological 
structure. The East River Mountain tunnel is at the right center of the image at Point A. Big Walker Mountain tunnel is 
at bottom center at Point B. 



72 



Figures 7 and 8 respectively are 1:200,000 scale 
enlargements of S-190A and color S-190B Skylab photographs of 
the area. These photos, acquired on 16 September 1973 before 
the autumn die-back of the vegetation, clearly show the 
Interstate 77 right-of-way and the two tunnel sites. Although 
these photographs have a higher resolution than the LANDSAT 
imagery shown in Figures A and B, interpretability for geolog- 
ical information is not as good because of the higher solar 
elevation and the dense vegetation over much of the area. 
However, the images do show the major structural features and 
tends to confirm the LANDSAT imagery analysis that the ridges 
at the two tunnel sites are continuous and that there appears 
to be no complications due to major geologic structural 
anomalies parallel to the tunnels. 



7.2 Radar Imagery 

NASA (see Appendix I) and the U.S. Air Force have acquired 
radar imagery of large portions of the United States over a period 
of several years. Large quantities of the Air Force acquired 
imagery are available to qualified users through the Goodyear 
Aerospace Corporation (see Appendix H). 



7.2.1 Carl in Canyon Site 

Two scales of the Air Force radar imagery were obtained 
of the Carl in Canyon area. Small scale imagery, with a swath 
width of 20 nm (37 km) was acquired with a military SC-01 
system on 3 May 1973. Larger scale coverage with a swath 
width of 10 nm (18.5 km) was taken with the same system on 
4 June 1971. Figure 9 shows the latter image enlarged to an 
approximate scale of 1:100,000. The major northeastern 
trending lineaments, points A and B identified on the satel- 
lite imagery, are further documented on the radar image at 
Points A and B. At this higher resolution, additional parallel 
lineaments are visible at Point C; this supports the hypothesis 
that the major lineaments are fracture or fault zones. The 
straight character of the embankment on the south side of the 
Humboldt River, Point D, and the parallelism of this embankment 
with the trend of the river at Points E and F supports the 
interpretation that this embankment is structurally conways 
at Points G, H, and I also support the interpretation that a 
major fracture system of this orientation exists in the area. 
An east-west trending lineament immediately south of the 
proposed tunnel site at Point J, if it proves to be a fault, 
could influence the geologic structure in the tunnel area. 

In summary, the evaluation of the radar imagery sup- 
ports the interpretations made from the satellite imagery. 

73 







Figure 7 - The major road network is imaged in sharp detail on this red spectral band S-190A Skylab image 
(no. 46-022). This photograph was acquired at an original scale of 1 :2,850,000, a small portion of which is 
shown here at a scale of 1 : 200,000. The geology is not as distinct on this photograph as on the lower reso- 
lution LANDSAT imagery shown in Figures 6A and 6B. The East River Mountain tunnel is at Point E and 
Big Walker Mountain tunnel at Point W. 



74 




Figure 8 -This scene (no. 88-056) of S-190B Skylab color photography (original scale of 1:950,000) has been 
enlarged to 1 :200,000 for purposes of comparison with Figures 6A, 6B, 7A, IDA and 10B. This photograph 
was acquired on September 1 6, 1973 at about 1 1 a.m. when the sun elevation was about 51 . This high solar 
altitude combined with the dense vegetation cover which was still vigorous minimized the amount of geological 
detail observable. As in Figure 7, the East River Mountain and Big Walker Mountain tunnels are at Points E 
and W, respectively. 



75 





Figure 9A and B - On this radar image the town of Carlin, Nevada appears on the left and the Carlin Canyon tunnel 
area on the right. This image, acquired at an original scale of 1 : 200 ,000 and enlarged to 1 :80,000, reveals a conju- 
gate joint set trending at nearly right angles to each other. One joint trend, the upper left, influenced the position 
of the channel of the Humboldt River at Points D, E, and F. Two major lineaments, A and B, differ somewhat from 
the established joint trend. These features appear to bracket the tunnel site and may represent faults. Compare 
this image with Figure 2 for the precise tunnel location. 

76 



The higher spatial resolution of this imagery adds structural 
detail and gives a further indication of the overall geological 
complexity of the tunnel site area. 



7.2.2 East River Mountain Site 

The radar image, Figures lOA and lOB, of the East 
River Mountain site, acquired with a 73 x H3 radar system on 
16 March 1962, is similar in appearance to the low sun angle 
LANDSAT imagery shown in Figure 6B. A more detailed geologic 
interpretation is possible using radar imagery because the 
spatial resolution and image contrast is substantially greater 
than for the LANDSAT image. This radar image covers both the 
East River Mountain and the Big Walker Mountain tunnel sites 
identified at Points R and S, respectively. The greater 
detail on the radar imagery makes it possible to identify 
sets of lineaments smaller than those visible on the LANDSAT 
image. These lineaments identified in the finely dissected, 
non-resistant rocks and soil aid in the regional interpretation 
of the fault patterns present. A comparison of the LANDSAT 
(Figures 6A and 6B) and radar images (Figures lOA and lOB) 
indicates that the structural character of the ridge penetrated 
by the tunnels is perhaps more easily assessed on the LANDSAT 
imagery. This is partly due to the lower contrast of the 
ridges on the satellite image and partly because the dip 
slope is illuminated on the LANDSAT imagery whereas it is a 
solid black shadow on the radar image. 

In summary, although a similar general assessment of 
the area can be made with either the radar or the LANDSAT and 
Skylab imagery, the overall geological structure in the area 
is better determined from the radar imagery. However, judgments 
as to the regional structural detail and continuity of the 
ridges penetrated by the tunnels are more readily made on the 
LANDSAT imagery. It should be noted, however, that the radar 
imagery used was of relatively low resolution and that modern 
unclassified systems are capable of producing much higher 
resolution imagery than that used in this evaluation. 



7.3 Low Sun-Angle Photography (LSAP) 

For many years geologists have recognized the value of shadow 
enhancement of topography for geologic structural analysis. 
However, photography used by photogeologists is almost always 
acquired for reasons other than geologic interpretation; usually 
photogrammetric purposes. Consequently, aerial photography is 
normally taken when shadow effects are minimal. It is only in the 
last few years that serious consideration has been given the use 
of LSAP. 

77 




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The objective of the LSAP investigation was not to simulate 
SLAR, but to shadow enhance the minor topography of the tunnel 
site for structural interpretation. 

The appropriate times of day for imagery acquisition for the 
first site studied, Carl in Canyon, were determined empirically by 
the field team during the first visit to the test site. Observation 
of shadow length and topography suggested a solar elevation of 
10°-15° above the horizon as being appropriate. 

The acquisition of LSAP requires somewhat more detailed 
planning than does conventional photography, and details for 
proper planning of a mission are given in Appendix D. The solar 
position or elevation changes at a rate of up to one degree eyery 
four minutes,!/ thus, timing is a critical factor. 

Although Clark (1971a) and Wise (1969) recommend a solar 
azimuth at right angles to the major structural features, this is 
not always possible to achieve. For instance, at the Carlin 
Canyon site which is at 40° N latitude, the annual extremes of 
solar azimuth extend over a range of only 70° for either morning 
or evening occurrences for an assumed solar elevation of 14°. 
The morning azimuths range from 70° on June 22 to 139° on December 
22 and the evening azimuths range from 290° on June 22 to 220° on 
December 22. Although this appears to limit the usefulness of 
LSAP, it should be noted that jointing nearly always occurs in 
conjugate sets which normally are at an angle to the regional 
structure. This fact implies that at least one joint trend will 
be reasonably well illuminated regardless of solar azimuth. Even 
if it is not possible to determine an optimum azimuth or the 
scheduling of LSAP missions is inflexible, useful geologic struc- 
tural information can still be acquired. Also, the geological 
information desired is not limited solely to structural data. 
Shadowing also enhances the drainage patterns!/ which aids in the 
interpretation of the type of surficial material present (see 
Appendix C). 



7.3.1 Carlin Canyon Site 

In the Carlin area, morning (Figures llA and 12B) and 
evening (Figures 12A and 12B) LSAP photography was acquired 



V The apparent rate of change of solar elevation of 1° every four 
minutes only occurs for those points on earth where and when the 
sun passes through the zenith. This is the maximum rate of change 
and can only occur for points between the Tropic of Cancer and 
Tropic of Capricorn, and then only twice a year. At all other 
places the apparent rate of change of solar altitude will be some- 
what slower. 

2/ Excessively low sun angles, as illustrated in Figure 12, obscure 
drainage detail. What constitutes "excessively low" however, is 
determined by the local topographic relief. 

80 




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on October 18, 1974. An attempt was made to acquire the 
photography when the solar elevation was between 10° and 15° 
above the horizon. The solar elevation was 11° for the 
morning flight; however, a delay of 20 minutes in the evening 
flight produced photography at a solar elevation of only 6°. 
As a consequence, many important topographic features were 
hidden in shadow (Figure 12). On this image, the area north 
of the Humboldt River shows a substantially better shadow- 
nonshadow ratio and more structural detail than other portions 
of the photograph because the regional slope in that area is 
5° to the west, which in effect produces a solar illumination 
angle of 11°. In this same general area near Point A on both 
Figures 11 and 12, many of the same lineaments are visible 
regardless of the change in solar azimuth. This increases the 
level of confidence one has in the features mapped. The 
lineament mapped on the LANDSAT image as Point G and on the 
radar image as Point B is evident on both morning and evening 
LSAP at Point C. On these photographs there is a suggestion 
that the feature may extend north of the Humboldt River. The 
lineament identified on the radar imagery at point J, Figure 
9B, is also visible on LSAP photography, at point D, and it 
appears that it could have geologic significance. No other 
fracture or fault through the tunnel site can be identified on 
this imagery. 

At the scale of the imagery, approximately 1:30,000, 
one can see the vertical bedding of the Diamond Peak conglom- 
erate on the western-most sunlit side of Carl in Canyon. The 
angular unconformity at the north bend of the Humboldt River 
is also visible. With information concerning the strike of 
the strata and the fracturing present in the area, it is 
apparent that the shape of Carl in Canyon is in part controlled 
by differential erosion parallel to bedding (Figure 11, 
Point B). 

The morning and evening LSAP, emphasize different 
sets of fracture trends, and both contribute to the under- 
standing of the geology of the area. 



7.3.2 East River Mountain Site 

Low sun angle photography of East River Mountain was 
acquired in the evening of April 5, 1974 and the morning of 
April 7, with a solar elevation of approximately 12°. The 
parallel nature of the sides of the flatirons on the dip 
slope is strongly emphasized, suggesting that they are 
controlled by fracturing and/or faulting. Other linear 
features are identifiable extending across the flatirons. 
One of these linear features (Figure 13, Point A), which is 
traceable through the south portal building site, was later 



83 





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84 



identified as a fault (see Plate II in pocket). Another 
lineament on the north slope of the East River Mountain lies 
to the west of the tunnel bore (Figure 14, Point B) and it 
too may represent a fault, but inadequate information is 
available from LSAP to establish this fact. It does, however, 
identify an area for further investigation by other remote 
sensors, ground geophysical methods, or drilling. 

The value of LSAP for revealing subtle land forms is 
apparent in Figure 15. Shallow sinkhole depressions are 
strongly enhanced and the linear orientation of many of the 
depressions is obvious, reflecting bedding and jointing. 

In summary, low sun-angle photography closely resembles 
radar imagery. When acquired with conventional metric 
camera systems, the LSAP imagery is at a substantially 
larger scale and of greater spatial resolution than radar 
imagery, and therefore complements, rather than replaces the 
radar. Valuable geological data can be acquired with LSAP 
in areas where the topography reflects the underlying geology. 
The results of this investigation, and others, suggests that 
this may occur in more instances than generally recognized 
from the use of conventional photography. 



7.4 Analysis Of Aerial Photography 

The investigation of the Carl in Canyon and East River Mountain 
test sites included three types of "conventionally" acquired 
aerial photography (black-and-white panchromatic, color, and 
"false" color infrared). 



7.4.1 Carl in Canyon, Test Site 

For the Carl in Canyon site the Nevada Highway Department 
provided black-and-white panchromatic photography at two 
different scales. One set of photography was acquired on 
July 25, 1974 at an approximate scale of 1:30,000. This 
photography complemented the satellite and radar imagery by 
providing a regional geologic setting of the tunnel site and 
a cognitive bridge between small-scale space imagery and 
large-scale aerial photography. The larger scale, 1:6,000, 
photography taken on May 9, 1974 was of utility for detailed 
site analysis. This photography was acquired when the vegetation 
was still in a vigorous growth stage and when the patterns 
of differential plant growth accentuated many geologic 
features, such as bedding and fractures. The time of acqui- 
sition, combined with the high resolution of black-and-white 

85 




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86 




Figure 1 5 - Low sun angles of illumination enhance subtle topographic features such as these small sinkholes located 
in the suburb of Bluefield, West Virginia. The alignment of sinkholes in this scene indicates control by both bedding 
and joint planes. 



87 



photography made it wery useful for identifying bedrock 
exposures and making geologic interpretations (see Figure 16). 
Color and color infrared photography was acquired on 18 October, 
1975 at scales of 1:30,000 and 1:6,000. At this time of the 
year, the vegetation in the area was largely dormant. Con- 
sequently, the strong infrared response characteristic of 
high vigor vegetation was not present, and the differences in 
vegetation vigor and growth patterns that might have provided 
clues to geologic structure were at a minimum (Figure 17). 
The natural color photography, particularly the large scale 
imagery (Figure 18), was of substantial value in delineating 
significant lithologic differences that were expressed by 
color. For the Carl in Canyon site, stereoscopic analysis of 
the large-scale black-and-white panchromatic and large scale 
color photography proved to be ^ery useful for geologic inter- 
pretation. 

At the beginning of the study the only geologic in- 
formation available for the Carlin Canyon test site was a 
"sketch" map of the tunnel area provided by the Nevada Highway 
Department. This map indicated an unconformable contact 
between the older conglomeratic Diamond Peak formation and the 
overlying Strathearn limestone formation. The map also iden- 
tified the large fault (designated F3, in Figure 16; and in 
Plate I; see pocket) just north of the east portal of the 
highway tunnel. In late 1975 the U.S. Geological Survey 
published a 1:125,000 scale geological map in Professional 
Paper 867-E. An enlarged portion of this map is shown in 
Figure 19. 

Faulting appears on both the black-and-white panchro- 
matic and color aerial photography as faint linear traces, as 
vegetational alignments, and as obvious stratigraphic offsets. 
On the panchromatic photography bedding of the formations is 
indicated by differences in tone. On the color photography 
the color emphasizes the lithologic differences and adds to 
the utility for analysis even where color differences are 
subtle (compare Figures 16 and 18). 

On the photography there are two sets of faults which 
may or may not have been contemporaneous. The major fault in 
the area, F3, trends northwest, subparallel to the strike of 
the formations. The plane of this fault appears nearly 
vertical where it is visible a few feet north of the east 
portal (see arrow on Figure 20). Several northeast trending 
faults cross the bedding at nearly right angles. At least one 
fault, F] , appears to displace the F3 fault in a right lateral 
sense. Most of the faults of this northeasterly trend do not 
appear to have appreciable offset, although one of these 
faults, Fo, does show stratigraphic displacement on the order 
of 100 feet (30 m.). 

88 




Figure 1 6 - Compilation of the analyses of all the remote sensing data acquired 
over the Carlin Canyon tunnel. This panchromatic photograph shows the 
combined results of the sensors used on this site. The dotted lines represent 
the unconformable contact between the Diamond Peak formation (MrPd) and 
the Strathearn limestone (rPPs). F„ is a major fault with as much as 400 feet 
(120m) of displacement at the east portal of the tunnel. Numerous other 
faults, marked by "F's," are mappable on photography. F- - is inferred 
from the analyses of both the small and large scale imagery. It is supported 
in places by field observations. 



89 




Figure 1 7 - Color infrared photography acquired on October 1 8 in the arid climate at the Carlin Canyon site contri- 
buted little information beyond that available from the natural color and black and white panchromatic photography. 
Compare this photograph with Figures 16 and 18. A lack of soil moisture and absence of growing vegetation (no 
precipitation for six months) minimized the value of color infrared photography in this area. 



90 




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R. 53 E. 1 16 00' 




EXPLANATION 




Permian and Upper Pennsylvanian rocks 
PIPu. undivided 

Puc, carbonate rocks, sillstone and much chert 
PIPs, Strathearn Formation 

UNCONFORMITY 



Pt 


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fm, Moleen Formation 
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sandstone 



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Diamond Peak and 
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V}Ad, Diamond Peak Formation 
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Mdc, undivided 

UNCONFORMITY 



Vinini Formation 
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Webb 
Formation 



From U. S. G. S. Professional Paper 8 6 7 - A 



Figure 19. Geological map of the Carlin Canyon, Nevada tunnel area. 




Figure 20 - This westward view to the immediate north side of the east portal of the Carlin Canyon 
tunnel shows the proximity (see arrow) of the major fault 
is highly fractured and considerably altered. 



F~. The limestone to the left of the fault 



93 



The limestone in the vicinity of the east portal is 
highly fractured and some faults, F5 and Fy, of the undeter- 
mined displacement are visible. Figure 21 shows the striated 
fault plane surface of fault, F^, exposed during clean-off 
above the east portal. This local area also shows deep wea- 
thering and alteration of the limestone. Consequently, 
competency of this rock material at the east portal does not 
appear to be as great as elsewhere and considerable problems 
could have been anticipated in construction as well as in 
maintaining the slope above the portal after construction. 

Two factors complicate the analysis of the geological 
structure in this area: 1) the high percentage of area 
mantled by a varied thickness of soil and talus, and 2) the 
lack of knowledge as to the precise nature of the unconfor- 
mable relationship between the Diamond Peak formation and the 
overlying Strathearn limestone. Studies of this unconformity 
reported in the U.S. Geological Survey Professional Paper 867- 
A indicate that the relationship varies from place to place; 
i.e., the strike of the two beds or formations are in places 
similar and in other places substantially different. For 
instance, at the north bend of the Humboldt River in Carl in 
Canyon, measurements above the road cut indicate that the 
strike of the two formations are identical, but the Diamond 
Peak formation is dipping 17° more steeply than the overlying 
Strathearn limestone. 

On the hillside to the south of the east portal of the 
highway tunnel, the Strathearn limestone is deposited over an 
irregular surface of the Diamond Peak conglomerate (Figure 
22). The basal limestone unit, i.e., the first limestone 
strata deposited over the old topography, appears to be draped 
over the old land surface. Younger strata, however, appear to 
have been deposited horizontally pinching out against the 
higher portions of the ocean floor. 

It is difficult to determine the validity of this 
interpretation. However, any other explanation of the re- 
lationships observed on the aerial photography would require 
an extremely complex history of strike-slip faulting. Al- 
though the simpler explanation appears more desirable, the 
latter interpretation should not be completely rejected. The 
major fault, F3, in the area appears to have had strike-slip 
movement. Possible fault, F11, south of the east portal, also 
may have strike-slip displacements. Because of the extensive 
faulting, the projection of the unconformity to tunnel level 
can only be approximated. 



94 




Figure 21 - This fault plane in the Strathearn limestone shows slippage striations (slickensides) exposed 
during the "clean-off" above the east portal of the Carlin tunnel. This fault, labeled F on Figure 16, is 
one of several faults of apparently small but undetermined displacement in this local area. 




Figure 22 - This view of the east side of the ridge or meander spur formed by the Humboldt River shows 
the steeply dipping strata and unconformity between the Diamond Peak conglomerate (left) and the 
Strathearn limestone (right). East Portal of the Carlin Canyon tunnel is visible on the right. 



95 



A recumbent fold on the north side of the river valley, 
a mile east of the tunnel site, graphically demonstrates that 
structure in the Carlin Canyon area is complex. Also, 400 
yards (366m) to the south of the west portal, a major, high- 
angle, reverse, Fi2» is identified on the geological map 
(Figure 19) and on the black and white panchromatic aerial 
photography of the test area. This fault has displaced the 
older Mississippi an age si Its tones and muds tones of the Webb 
formation over the younger Diamond Peak conglomerates. 



7.4.2 East River Mountain Tunnel Site 

The East River mountain site, which receives 40-60 
inches (100-200 cm) of annual rainfall, is densely wooded. 
Consequently, it was necessary to acquire both photography and 
scanner imagery of the site while there was no leaf canopy to 
obscure the ground surface in the tunnel area. 

The West Virginia Department of Highways provided 
panchromatic photography of the area, at a scale of 1:12,000. 
The dates of the overflights for this imagery are not known 
but they were made during early construction phases of the 
tunnel and at a time when the vegetation obscured much of the 
surface detail essential for accurate geological mapping. 

Color and color infrared photography taken on 5 and 6 
April 1975, had to be reflown because of technical deficiencies 
Due to winds and cloudy weather, reflying was not accomplished 
until 27 April. Portions of the color infrared photography 
from the earlier date (Figure 23A) were usable. Comparison of 
this photography with the color infrared photographs from the 
April 27 flight (Figure 23B) shows the rapid development of 
the deciduous vegetation in the spring. In the photograph of 
the later date, the leaf cover, although only partially 
developed, appears to have obscured much of the ground. The 
color infrared photograph from the 6 April overflight shows 
only minor amounts of green vegetation (red coloration) in 
some of the lower meadows and fields, thus, any geologic 
structure, such as faults, that may be enhanced by differ- 
ential vegetational growth rates are not evident. Three weeks 
later, (27 April) the leaf cover is nearly universally pre- 
sent, except near the upper part of the mountain, and again no 
emphasis of jointing or fracturing is apparent. The absence 
of such indications is probably due to the abundant rainfall 
which occurred throughout the late winter and early spring. 



96 





Figure 23 - Color infrared images of the East River Mountain site taken three weeks apart. Scene A was 
taken on 6 April before vegetation development. Scene B was acquired on 27 April. In this short interval 
the trees "leafed out" to the extent that the entire area shows high infrared reflectance. This illustrates 
the critical timing required for some remote sensor missions to obtain optimum data. 



97 



Two scales of color and color infrared photography 
were flown. The photography shown in Figures 23A and 23B is 
at a scale of 1 :30, 000 which is excellent for a synoptic 
view of the area, but somewhat small for detailed geologic 
analysis. Large scale photography was flown at an altitude 
of 3,500 feet (1066 m) AMT (above mean terrain). The detail 
provided by this photography is good for geologic analysis, 
however, the topographic relief of the mountain produces a 
parallax in this larger scale imagery that is too extreme 
for comfortable stereoscopic viewing. East River Mountain 
is approximately 1,000 feet (306 m.) high which is over 28% 
of the aircraft altitude used, consequently the scale of the 
photography ranges from 1:7,000 for the valleys to 1:5,000 
for the mountain top. A flight altitude of 6,000 feet 
(1,835 m) would have been a better choice as a compromise 
between image scale and resolution of surface detail. In 
spite of the difficulty of viewing, the stereographic photo- 
graphy provided excellent detail for analysis of the stratigra- 
phy and structure, particularly on the dip slope of the 
mountain. 

Few rock outcrops exist in the area, except for the 
resistant Tuscarora sandstone which forms the caprock of the 
mountain (Figure 24). Here the thick sandstone unit forms a 
vertical cliff along most of the mountain crest. Although 
the rock has no soil cover, it is nearly 100% lichen covered. 
Figure 25 illustrates what may be considered a typical 
exposure. In many places a leathery species of lichen 
produces an even thicker cover on the rock. 

A natural color photograph, (Figure 26), taken at the 
same time as the color infrared photograph in Figure 23B, 
does not show the pronounced effects of leaf canopy development 
and the deciduous trees appear essentially bare. This 
photography, both the large and small scale, was used for 
most of the photo interpretation of the tunnel site. The 
large scale imagery was a valuable tool for mapping the 
various stratigraphic horizons and structure. It was possible 
to locate accurately the different stratigraphic horizons 
and faults of small displacement. Two faults were positively 
identified in the vicinity of the tunnel. Several other 
lineaments may be faults or joints with no displacement. 

Fault, F] , shown on Plates II and V (see pocket) was 
tentatively identified on LSAP photography. Its presence 
was further substantiated in the photo interpretation phase 
of the analysis. This fault should have little or no effect 
on the tunnel construction, but the south portal building 
appears to be on the fault trace. 



98 




Figure 24 - The highly resistant Tuscarora sandstone is shown in this view along the crest 
of East River Mountain. This sandstone is the major ridge forming strata in the region. 
Note the vertical cliff which is in places nearly 50 feet (15m) high. 




Figure 25 - Lichens are ubiquitous on rock outcrops and seriously interfere with lithological 
discrimination by remote sensing methods in southern Virginia-West Virginia. Here an outcrop 
of Tuscarora sandstone is completely covered with lichens. This is typical of over 95% of the 
rock exposures not disturbed by man's activities. 



99 




Figure 26 - Natural color stereogram of the East River Mountain site. It was taken simultaneously 
with Figure 23B, indicating that although the leaf canopy had started to develop, much of the 
ground surface was still exposed. Stereoscopic viewing of this stereogram (and larger scale 
photography) permitted the detailed delineation of the stratigraphy and structure in the area. 



100 



Fault, F2, which lies mostly outside the area of 
interest has an undetermined displacement. It has an estimated 
ten foot {3m) displacement on the ridge crest. Displacement, 
however, appears to increase to the south and several tens 
of feet of strati graphic offset appears probable where it 
extends into the map shown on Plate II. 

Linear feature, F3, if a fault, does not extend to 
the crest of the ridge, but displacement appears possible 
where it crosses younger strata outside the map area. This i 

feature does not appear to extend to the tunnel alignment. | 

Linear, F4 is another probable joint. It parallels the 

dominant joint pattern in the area and seems to be an extension || 

of a fracture identified on the dip slope outside the mapped ij 

area. | 

The upper two-thirds of the north slope (scarp slope) I 

of the mountain is composed of relatively non-resistant ij 

siltstones, shale and shalely limestones of the Juniata and I 

Martinsburg formations. The contact between these two i 
formations is not identifiable on the photography and the 

boundary shown on the cross-sections (Plate II) is based on 1 

the tunnel contractor's preconstruction site report. On the j 

photography, there is an identifiable topographic break, j 

some distance below the supposed basal contact of the Juniata. || 

This topographic break, apparently created by a more competent ij 

horizon within the Juniata, is the only distinguishable Ij 

stratigraphic feature on the scarp slope. 'i 

The dense limestone present at the north portal is { 

easily eroded in the present moist environment and, conse- j 

quently, is a valley forming unit. It contains numerous Ij 

sinkholes which are easily identified by stereoscopic exam- | 

i nation of the photographs (see the stereogram in Figure I 

26). I 

From the aerial photography it is possible to judge 
that the soil cover on the south slope (dip slope) of the 
mountain is relatively thin, probably less than 3 feet (1 
m.) thick. Soil thickness on the north slope is more dif- 
ficult to judge. The lower portion of the slope, consisting 
of limestones, has a thin soil cover of only a foot or two 
(.3-. 6 m) in most places. The upper slope, below the sand- 
stone escarpment, appears to be covered with soil and weathered 
shale with an estimated thickness of as much as 10 to 20 
feet (3-6 m) . 

The sinkholes near the north portal indicate subterranean 
drainage and solution cavities. The presence of such features 
could indicate a need to fill the voids for structural 
strength and to prevent the inflow of water. 

101 



On the south side (dip slope) of the mountain the 
prominant jointing in the Tuscarora, Rose Hill and Keefer 
formations could be avenues for water percolation to depth. 
This could cause a water problem for approximately the first 
1,200 feet (366 m) of tunnel construction from the south 
portal . 

The Rocky Gap formation, which crops out at the south 
portal is, in most places, a resistant sandstone unit. 
Locally, however, the cementing material has been leached 
away leaving a soft friable sand. 



7.5 Multi-Band Photography 

Multi-band photography is a technique of simultaneously 
obtaining black-and-white photographs of a target using filters 
for several bands of the visible or near-visible portions of the 
spectrum. The theory of multiband sensing is that objects reflect 
energy of varying intensity in different portions of the spectrum, 
unless the object is pure white or pure black. Once the spectral 
"signature" of an object has been determined, it should be pos- 
sible to acquire appropriately filtered imagery that will differ- 
entiate the object from the background and, thus, enable objects 
to be identified and described. Each photograph can be studied 
individually or in combination on a color additive viewer to 
provide a natural color or a range of false-color composites 
which may improve the interpretability of the image. Several 
investigators have evaluated the use of multi-band photography 
for discriminating rock types (Marrs, 1973; Longshaw and Gilbert- 
son, 1975 and others). Most of the results attained with multi- 
band photography show only moderate success in discriminating 
lithologies or the results were not sufficiently better than 
those derived from conventional photography to justify the addi- 
tional cost of multiband photography. Such conclusions, plus 
economic considerations, eliminated airborne multi-band photo- 
graphy from the current investigation. Also, we felt that the 
multi spectral scanner would provide an adequate assessment of the 
utility of the multispectral imagery for rock identification even 
though the resolution of the MSS imagery is inferior to photo- 
graphy. However, during the actual imagery analysis there was 
difficulty in discriminating the Diamond Peak conglomerate and 
Strathearn limestone using color aerial photography and multi- 
spectral imagery of Carl in Canyon. The difference in color of 
the two rock types is not pronounced; one being light yellow 
brown and the other gray. Both rocks have appreciable lichen 
cover, some of which has turned bright orange, thus, both rock 
types appear similar in color when viewed from a distance. The 
weathered surfaces, plus a partial coating of lichen growth, 

102 



tends to mask the true spectral response of the rocks. Figures 27 
and 28 are, respectively, ground photographs of typical exposures 
of the Diamond Peak conglomerate and the Strathearn limestone. 
This prompted field spectroradiometric measurements of the reflec- 
tances of the two lithologic units. At this point it was also 
decided to include multiband photography taken from ground stations 
as part of this expanded study effort. 

Multiband photography of three selected target areas was 
acquired on October 23, although rapidly moving cloud shadows 
interfered somewhat. The different spectral band exposures were 
made sequentially using a 4" x 5" press camera. Only a few 
minutes separated the exposures and it is felt that this slight 
time lapse had little effect on the documentation of the spectral 
response of the rocks. However, cloud movement between exposures 
produced bizarre colors in cloud and shadow areas on the color 
composite images. 

Kodak Tri-X Pan Professional film No. 4164 was used with 
Wratten filters Nos. 26 (red), 48 (blue) and 58 (green). High 
Speed Infrared film No. 4143 was exposed with Wratten filters 
Nos. 29 and 55 combined. Figure 29 shows the relative spectral 
transmittance of the filters and the film response. The visible 
band imagery was properly exposed but the infrared film was 
overexposed to the extent that a reliable evaluation of the 
utility of that spectral band could not be made. Positive 
transparencies of the multiband imagery were studied with the aid 
of an additive color viewer. 

Various combinations of color coding and color intensity 
were tested in an attempt to increase the interpretability of the 
conglomerate and limestone units. The final judgment was that 
the natural color display presented the best lithologic discrim- 
ination. Although a one-to-one comparison cannot be made between 
the ground multiband photography and the color aerial photography, 
the multiband color composite. Figure 30, shows substantially 
better color saturation than does the large scale color aerial 
photography (Figure 18) taken at an altitude of 3,000 feet (914 
m). Based on this series of comparisons, lithologic differentiation 
can be made more confidently on the multiband color composite 
photograph than on the color aerial photograph. 

To further test the information content of multiband photography, 
photo ratioing techniques, similar to those developed by Piech 
and Walker (1971a, 1972a, b and c) were used. A series of black 
and white, high, medium, and low contrast positive and negative 
transparencies were made of the red, green, and blue spectral 
band photographs. These were sandwiched in various combinations 
to mask out a single rock type and thus accentuate the imaging of 
the other rock type. 

103 




Figure 27 - The weathered surface of the Diamond Peak conglomerate is shown on this 
photograph (silver dollar gives scale). The rock surface, which consists largely of chert 
pebbles is partially coated with a lichen growth and discolored with a thin coating of 
desert varnish. 




**-': oN 






'^ 







^•^.^ i 



Figure 28 -This photograph of the Strathearn limestone, typical of outcrops near the 
top of the ridge, shows the limestone weathers to a light gray (silver dollar scale). 
Lichens coat the surface in varied amounts and the bright orange color of the lichen, 
when viewed at a distance, contributes to an appearance similar to the conglomerate 
surface. This photograph, however, is deceiving in that much of the light colored 
surface is actually covered with lichens which bleach white when they die. 



104 



600 



700 



800 



100% - — 




300 



400 



"1 r 

500 600 

WAVELENGTH (nanometers) 



700 



800 



Figure 29A illustrates the relationship of the spectral sensitivity of Kodak Tri X Pan Professional Film, 
which is relatively flat from 380 to 640 nanometers, to the spectral transmission of the three Wratten 
color separation filters used. The blue filter, W. 48, has a peak transmission of 33% at 460 nm., with 
half-peak transmissions at 430 and 490 nm. These values for the green filter, W.58 are, peak of 54% at 
530 nm., and half-peak at 505 and 560 nm. The red filter, W. 26, half-peak occurs at about 605 nm; 
78% is reached at 620 nm. and 86% at 640 nm. Beyond this point the film sensitivity is essentially zero. 



100% 



.10% 




500 



600 700 

WAVELENGTH (nanometers) 



800 



900 



Figure 29B illustrates the relationship between the spectral sensitivity of Kodak High Speed Infrared 
Film 4143, and combined characteristics of Wratten filters 29 and 55. These filters, when combined, 
begin to transmit at about 695 nm., with 25% transmission at 700 nm. and a maximum of 90% at 800 
nm. The film sensitivity peaks at about 800 nm.; the half-peak points of the film/filter combination are 
are approximately 710 and 900 nm. 

105 




Blue image (Wratten filter No. 48) 





>iiP^^^^^'ZS!f 



"k 



Green image (Wratten filter No. 58) 



• *'-°*'*»* 



■» f > 



'^^^ 



Red image (Wratten filter No. 26) 



^U^^*^*^ 



Infrared image (Wratten filters Nos. 29 + 55) 




Figure 30. This color composite image was produced by combining the black and white images above with the 
appropriate color filters. This type of photographic processing permits the adjustment of the saturation of 
each color to produce the best discrimination of rock types. 



106 



Figure 31 represents the best results of the wide variety of 
combinations tested. This image is a product of sandwiching a 
high-contrast, red band positive; a low-contrast, green band 
positive; and a low-contrast, blue band negative. Similar results 
were obtained with a low-contrast, red band positive and a high- 
contrast, blue band negative, but better differentiation is 
possible with the multiband color composite image shown in Figure 
30. 



This test is considered only an indication of the full 
potential of multiband photography because the acquisition of the 
photography was not adequately controlled, the filters used were 
not necessarily the best choices, and the imagery was not analyzed 
exhaustively. The results do justify further investigations. 

Large scale, multiband aerial photography of tunnel sites 
acquired using the new Kodak Multispectral Infrared Aerial film, 
SO 289 would permit the reconstruction of both natural color and 
standard color infrared (false-color) images as well as a variety 
of other false color presentations. With this approach only one 
camera would be required to produce the results of all the dif- 
ferent film products normally used. The results obtained with 
such imagery, properly filtered, can be expected to be as good, 
and possibly better, than with conventional color and color- 
infrared films of comparable scale. 




Figure 31 - Photo "masking" techniques were tested with the multi-band images shown in 
Figure 30. This consisted of making positive and negative transparencies of various densities 
of each spectral image. These were sandwiched in various combinations in an attempt to 
mask out the Diamond Peak formation and enhance the Strathearn limestone outcrops. 
These tests were not successful. 

107 



7.6 Multi spectral Scanner (MSS) Imagery 

For many years physicists have known that different objects 
have unique reflectance and emittance characteristics. If these 
differences in energy levels are sensed in enough narrow spectral 
increments, theoretically, a unique "signature" for each object 
could be identified. The imaging of a scene in a series of dis- 
crete narrow spectral bands is possible with electro-mechanical 
systems. Recording of such data on magnetic tape provides a flexi- 
bility in analysis and interpretation difficult or impossible to 
obtain with photographic systems. If a diagnostic "signature" for 
a particular target exists within the spectral limits of the system, 
computer processing can be used to differentiate the target and the 
background. For instance, ferric iron bearing rocks normally 
appear reddish because rocks absorb the blue and green portions of 
the spectrum and reflect the red. Imagery filtered to sense only 
the red portion of the spectrum should show the iron bearing rocks 
as brighter targets than the non-iron bearing formations. The 
contrast can be further enhanced by producing a computer ratioed 
red/blue image (Vincent and Thompson, 1972b). 

Goetz (1975), Vincent et al., (1973) and other investigators 
have obtained impressive results applying similiar computer pro- 
cessing techniques to LANDSAT imagery which is separated into 
green, red, and two near-infrared bands. Goetz et al . , (1975) were 
able to enhance subtle differences in rock types and recognize 
zones of weathering and alteration, particularly in igneous rocks. 



7.6.1 Carl in Canyon Test Site 

The ground surface at the Carl in Canyon test site 
consists principally of limestone and chert pebble conglo- 
merate and the resulting soil products of both formations. 
Minor amounts of siltstone shale and coarse sandstones are 
interbedded with the conglomerate. Minor beds within the 
conglomerate contain hematite (Fe20o) and are colored various 
shades of red. Locally, the cementing material in the con- 
glomerate also contains considerable limonite (HFeOp)* and 
where this occurs, the rocks and soil appear yellowish. The 
more intensively colored areas are identifiable on the color 
aerial photography. With few exceptions, the two rock types 
are similiar in appearance from a distance. An almost com- 
plete covering of living and dead lichen increases the similar- 
ity in appearance. 



108 



Multi spectral imagery of the site was acquired on 
October 18, 1974, (see Appendix F for system description). 
Imagery in ten spectral bands was acquired simultaneously 
over a spectral range extending from the near ultra-violet 
into the near-infrared. Table 3 lists the tape channel and 
spectral bandwidths recorded. 



Table 3 Multispectral Channels and Bandwidths used in this Investigation 



Channel 


Bandwidth (ym) 


1 


.38-. 42 


2 


.42-. 45 


3 


.45-. 50 


4 


.50-. 55 


5 


.55-. 60 


6 


.60-. 65 


7 


.65-. 69 


8 


.70-. 79 


9 


.80-. 89 


10 


.92-1.1 



Densitometry of Multispectral Images 

Images from the individual spectral bands look similar 
with only minor exceptions as shown in Figure 32. These 
images are spot samples in the spectral range of blue (.45- 
.50ym), orange (.6-.65ym), red (.65-.69ym) and near infrared 
(.80-.89ym). This lack of difference in spectral brightness 
tends to confirm photometric field studies made by Rains and 
Lee (1975) on a variety of rock types. 

In order to determine the relative brightness of several 
sets of targets, a series of points known to represent dif- 
ferences in lithology were selected within the imaged area. 
Paper positive strip prints of single channel, channel 
ratios, channel combinations, and combination ratio images 
were used for analysis. Using a Macbeth, densitometer. 
Model TD 504, an extensive series of photographic density 
measurements were made and evaluated in an attempt to: 

1. Determine the relative brightness of critical 
outcrop areas in each channel of spectral data 
(Table 4). 



109 




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Figure 32. The soil and rocks of the Carlin Canyon area shown in these multispectral scanner images, 
display similar reflective characteristics over a wide spectral range. Figure A was acquired in the 
spectral range of .45 - .50 um, B in .60 - .65 um, C in .65 - .69 um and D in 30 - B9 um. Compare 
images A and B with Figure 34 which is a ratioed image of B/A. 



110 



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2. Establish that the resultant relative brightness of 
combinations of channels are logical developments 
from their "raw" image data. 

3. Select a set of channel combinations of the original 
taped data to produce images that would optimize the 
relative brightness differences. 



Additive Color Enhancement 

A series of images from channel combinations selected to 
simulate LANDSAT spectral bandwidths were combined to simulate 
(a) normal color, (b) color infrared, and (c) very "false- 
color" to maximize the spectral differences. 

As one can see in the aerial color photograph of the 
Carlin Canyon test site. Figure 18, there is little variation 
in the uniform light yellow brown to white color over the 
area. The reconstruction of natural color imagery, (Figure 
33) produced from the proper combination and color coding of 
the appropriate spectral bands, did not produce significantly 
different information. The image does, however, demonstrate 
some of the versatility of multiband imagery. A color infra- 
red multiband composite, also did not provide additional 
useful information for structural analysis or discrimination 
of rock types. The latter result, however, is judged to be 
largely due to the season in which the data was acquired. 
Consequently, these examples should not be interpreted as 
condemning the use of additive color processing of multi- 
spectral imagery. Because additive color viewers permit the 
selection of color filters and the intensity of light to be 
used in viewing each spectral band image, features of interest 
can usually be exhibited in greater contrast than they appear 
on natural color photography. 



Spectral Band Ratioing 

A number of computer ratioed images were made in an 
attempt to enhance geologic features in the area. These 
efforts concentrated on enhancing faults and fractures and on 
lithological discrimination. Most of this type of processing 
was restricted to the Carlin Canyon site because rock outcrops 
were more extensive and visible at this site than in the East 
River Mountain area. The most significant result was the 
enhancement of the ferric iron bearing zones. Ratios of the 
.60-.69ym band or .60-.65ym band to the .45-.50ym band appear 
to provide the best discrimination of ferric iron. The 
latter ratio provides somewhat better image contrast or 
enhancement and is shown in Figure 34. Areas of concentration 
of ferric iron are imaged as above average in brightness; 

112 




Figure 33 - Color composite image from the multispectral scanner 
imagery produced by printing spectral bands .42-.50um in blue, 
.50-.60um in green and .60-.69um in red. Because the spectral 
"cutoff" characteristics of the grating in the multispectral scanner 
is much sharper than that of the color film, the color of this image 
only approximates that of Figure 18. This does, however, illustrate 
some of the versatility of multispectral scanner imagery. 



113 





Figure 34 - Ratio image produced from spectral bands .60-.65um/.45-.50um. The resulting 
image emphasizes in lighter tone the ferric iron zones in the Diamond Peak conglomerate. 
Compare this image to Figures 32A and B from which it was produced. Points d, e, f, and 
g can be seen in Figure 18. 



114 



the lighter the image tone, the greater the iron concentration. ! 

The more obvious areas are at Points A, B, C, D, E, F, and G. ; 

All of these bright areas are restricted to the Diamond Peak |' 

conglomerate outcrops with the exception of Point C which is i' 

freshly exposed alluvial terrace gravels of probable Pleistocene j 

age. These terrace deposits are reddish toned and contrast E 

with the overlying light gray limestone talus (see Figure -j 

18). ! 

Several combinations of the ratioed images were examined i 

with an additive color viewer. The combination which provided ! 
the most contrast between the limestone and the conglomerate 

was used to produce the image shown in Figure 35. The | 

letter designations shown on Figure 34 will be used in the | 

following discussion concerning this color composite image. '! 

In Figure 35, the distribution of the yellowish-orange 'i 

areas should be compared with the geologic map over print in I-; 

Figure 16. It is evident that Figure 35 is predominately |i 

blue on the right and reddish on the left which roughly is || 

the distribution of the Strathearn limestone and the Diamond ,!; 

Peak conglomerate. However, the contact as shown in Figure i; 

16 does not coincide with the distribution of the two colors |i 

in Figure 35. Examination of Figure 16 and the color stereogram, li 
Figure 18, shows that Points D, E and F are separated by 
talus material eroded from the overlying limestone, which 

appears as blue. Much of the west slope of the spur is also i? 

mantled with talus from the limestone ridge. Points A and B J 

are exposures of the conglomerate beds in which the iron :| 

appears predominantly limonitic and yellowish in color. ij 

Points D, E and F are hematitic and all are reddish, particularly |i| 
Point F. Point C is the exposed iron bearing terrace materials 
overlain with limestone talus. 

The faint yellowish streaks to the east of the Humboldt 
River at Points H and I occur on limestone talus slopes. 
Field examination of these points indicated that numerous 
limestone cobbles and pebbles were stained with a thin 
ferric iron coating. This indicates the high degree of 
sensitivity of this system for the detection of ferric iron. 
Another point of passing interest is that the Pinon pines 
present on the hillsides to the north of the river are 
imaged as white. 

In summary, the densitometric studies and the ratioing 
and additive color processing of the multi spectral imagery 
made in this study established that there was little if any 
spectral difference between the limestone and the conglomerate 
formations in the area except where localized reddening of 
the conglomerate could be easily found as bright hazy spots 

115 




Figure 35 - This color composite image was constructed from tliree ratioed images as follows: 
blue from .45-. 55um/.65-.79um, green from .60-.69um/.70-.79um and red from .45-.55um/ 
.65-.79um. Here, the presence of ferric iron is emphasized by varied shades of yellow and orange. 



116 



in areas on a .55-.60ym/.50-.55ym or a .60-.65um/.45-.50um 
ratioed image. With the color-coded, ratioed images, the 
lithologic discrimination of the materials is more pronounced 
than on any other type of imagery. 

Spectroradiometric Investigations \ 

I 

To further calibrate the airborne data two series of 

reflectance measurements were made in August 1975 with an | 

ISCO scanning spectroradiometer and in October 1975 with two .{ 

Exotech four-band radiometers filtered to correspond in I 

bandwidth to the spectral range of the four LANDSAT multispectral I 

scanner channels. The details of these investigations are \ 

presented in Appendix E. I 



7.6.2 East River Mountain 

Visible and near-visible multispectral scanner imagery 
of the East River Mountain was acquired near noon on 1 
April, 1975. Single channels of data provided no significant 
information that was not available from the aerial photography. 
Also, ratioing of various spectral bands did not appreciably 
increase the geologic information that could be extracted. 

Of only casual interest to tunnel site studies, a 
ratio of bands .60-. 69 ym/.80-.89 ym greatly increased the 
discrimination between evergreen trees from the dormant 
deciduous vegetation cover. Pine trees are scattered over 
much of the south slope of the mountain and only locally do 
they occur in groves. The high reflectance of the evergreens 
as measured in the infrared band, when ratioed with the low 
reflective response in the red band, markedly enhanced the 
image contrast of these trees. 



7.7 Thermal Infrared Imagery 

Imagery acquired in the 8-14 ym spectral band can provide 
unique geologic information. The type of information derived 
depends in part on the system used. Thermal scanners are available 
with single detectors which sense energy emitted throughout the 
8-14 ym atmospheric window or filters can be used to restrict or 
divide the bandwidth sensed. Some systems have the capability of 
simultaneously sensing in 2 or 3 bandwidths that are narrower 
than the full 8-14 ym window. Such systems permit manipulation 
of the data by computer processing to extract geologic information 
not evident on a single channel of data. 

117 



A two-channel thermal scanner system was used for this in- 
vestigation. The spectral bandwidths sensed were 8-10 ym and 10- 
12 ym (see Appendix F for more detailed information on the 
system) . 

Thermal scanner imagery was acquired of the eastern and 
western test sites within 24 hours of the overflight for the 
multispectral scanner data. The same scanning system was used to 
acquire both types of imagery, but equipped with appropriate 
detectors and filters for the different missions. Overflights 
for thermal imagery were made during the day and at night. 
Daytime thermal imagery is generally considered not to be as good 
as night time imagery for most purposes. However, for detecting 
soil moisture by the effects it has upon the apparent temperature 
of the ground surface, daytime imagery has proven to be useful. 
Thus, daytime overflights may be valuable for the detection of 
water concentrations in fracture zones and faults. Further, 
daytime differential solar heating of the irregular ground surface 
produces pseudo-shadow patterns which appear similar to low-sun- 
angle photography. 



7.7.1 Carl in Canyon Test Site 

Thermal imagery of the Carl in Canyon site was acquired 
on October 17, 18, and 19, 1974. Daytime temperatures 
ranged from 70° to 75° F. (21° to 24° C) and night time 
temperatures dropped to 32° F. (0° C) by 10:30 in the evening. 
Night time overflights were made on October 17 at about 
11:30 p.m. There was a question as to the quality of the 
recorded data from this flight, and the flight was repeated 
before dawn (6:30 a.m.) on October 19. Daytime thermal 
imagery was acquired at about 10:45 p.m. on October 18. 
During each of the missions, overflights were made at two 
different altitudes. A single overpass made at an altitude 
of approximately 6,000 feet (1828 m.) provided a synoptic 
view of the area. Multiple overflights made at an altitude 
of approximately 3,000 feet (914 m.) obtained the desired 
detail concerning the geology of the test site. At this 
site the larger scale imagery flown in overlapping flight 
lines allowed the imagery to be viewed stereoscopically. 
Stereoscopic viewing of thermal imagery can be useful in 
analysis although it is not an essential requirement if, as 
it should be, the thermal imagery is analyzed in conjunction 
with aerial photography. 

The majority of the analyses conducted on the Carl in 
Canyon imagery was with Flight Line D from the mission flown 
just before midnight on October 17. A number of different 

118 



processing techniques were used on the data (see Table 16 in 
Appendix F). 

Little difference between the two spectral bands could be 
detected by visual examination on the imagery. Neither 
spectral band showed any lithologic discrimination between the 
limestone and the conglomerate, although the thermal inertia 
properties of the solid rock outcrops caused them to be imaged 
as warmer than the adjacent soil cover. Figure 36 is an 
example of the 8-10 ym band image. Because of the outcrop and 
soil patterns the angular unconformity between the Diamond 
Peak conglomerate and the Strathearn limestone is prominent 
and easily recognized in the bend of the river. For the same 
reason some of the minor faults and fractures can be seen to 
the north of the east portal of the tunnel. 

A ratioed image (8-10 ym/10-12 ym) from the midnight 
overflight was rather disappointing. As previously discussed 
silica (Si02) exhibits an emission minima in the 8-10 ym 
range, therefore, diagnostic information relating to the 
silicia content of the Diamond Peak formation should be 
derivable from this ratioed image. The discrimination of 
siliceous rocks by thermal image ratioing does not rely on 
thermal contrast between rock types, but upon emission minima 
produced by silica in the 8-10 ym band. When the signal 
levels of the two channels are essentially equal, which is 
true for most materials, the value of the ratioed signal will 
be near unity and all such features will appear as a uniform 
gray tone on the image. Those features that produced differ- 
ent voltage levels on the individual taped channels will 
appear either lighter or darker in the ratioed image. 

As mentioned in Section 7.5 and illustrated in Figures 27 
and 28, both rock types have appreciable lichen cover. The 
weathered surfaces, plus the partial coating of lichen growth, 
tend to mask the true spectral response of the rocks and 
minimize the emission differences anticipated between the 
silica rich conglomerate and the limestone. 

The image shown in Figure 37 was made from the predawn 
thermal data. This ratioed product reveals substantially more 
significant geologic detail than that from the midnight data 
in spite of the light and dark tone banding across the image 
produced by "bounce" in one of the detectors ("bounce" occurs 
when one of the detectors does not maintain a constant base 
level of response) . 



119 




Figure 36 - The high thermal contrast between the rock outcrops and the adjacent soil 
on this 8-1 Oum thermal infrared image is due to the high thermal inertia properties of 
the dense rock material. No discrimination between the two dissimilar rock lithologies 
is possible on this image. Some anomalous linear features can be identified because of 
the rock-Goil thermal contrast. 



120 




Figure 37 - Silica bearing rocks exhibit an emission minima in Xhe 8-10um range and 
should appear dark on this 8-10um/10-1 2um spectral band ratioed image. This was 
partially accomplished on this image. See the text for details concerning the annota- 
tion. 



121 



Points a and b on this image represent the Diamond Peak 
conglomerate and the Strathearn limestone, respectively. 
Although differences are not pronounced, the more siliceous 
conglomerate appears somewhat darker on this image. Point c 
is an island in the Humboldt River, barren of vegetation, 
which consists predominantly of silica sand, consequently, it 
appears dark on the image. Points d and c lie on the contact 
between the two formations. The dark streak at Point d is a 
chert conglomerate bed. Point f is an area that was disturbed 
by a bulldozer. This area was excavated to considerable depth 
and refilled, and no doubt, the soil exposed in this area 
contains a higher percentage of silica than the surrounding 
limestones talus. Point h is on the trace of the large fault 
that separates the Strathearn limestone from the Diamond Peak 
formation (F3 on the map in Plate I and Figure 16). The area 
designated by h is anomalous and could not be resolved with 
the remote sensor imagery. A field check indicated that it is 
an area of concentration of chert pebbles and sand material 
weathered from the Diamond Peak formation. It is topographi- 
cally slightly higher than the surrounding area, thus, the 
material has not been contaminated with limestone debris. The 
darktoned arcuate area designated Point g is also anomalous 
and probably cannot be explained without detailed soils 
analysis. The dark zone coincides with a minor drainage 
channel on the hillside. Field examination disclosed that 
there are small outcrops of the Diamond Peak conglomerate in 
this channel, however, the rock exposures are not continuous 
and soil material forms the bed of the remainder of the gully. 
It is surmised that this soil, although similar in appearance 
to the surrounding area, contains a higher percentage of 
siliceous sand. There is also less vegetation present. 

The difference in tone between Points n and (Figure 
37) mark the large fault F3 shown on Figure 16. The fault 
trace here is somewhat more clear than on the aerial photo- 
graphy. Point m marks the river terrace material and Point u, 
the limestone talus exposed when the west portal was excavated. 
The underlying terrace deposit contains substantially more 
quartz sand than the overlaying talus, consequently. Point m 
is imaged much darker than the remainder of the area. Points 
s and j are slightly darker bands which are outcrops of con- 
glomerate beds. 

Points 1 and k lie in an area of the highly siliceous 
Webb formation. The line between these two areas is a gully, 
the sides of which are quite steep. Field examination of this 
area indicates that area 1 has more soil cover then does area 
k. Consequently more siliceous rock fragments are exposed on 
the surface in area k accounting for the darker tone. Point t 
marks the fault F11 shown on Figure 16. The dissimilar 



122 



appearance of the areas along this line is in part due to rock 
texture or size of the material exposed at the surface, and in 
part due to a greater development of soil cover to the north 
of Point t. Point v marks the fault, F12 shown on Figure 16 
and the trace here can be identified for the same reasons. In 
neither case can the full extent of the fault be drawn on the 
basis of this image. The white spots on the road are ve- 
hicles. 

In summary, the pre-dawn data produced substantially 
better results than that produced from the data acquired at 
midnight. The ratioed image from the pre-dawn overflight 
contains substantially more geological information than does 
either single channel image. Some of the information is as 
well or better expressed on this image than on any other 
remote sensor data product. 



7.7.2 East River Mountain Test Site 

Thermal imagery of this site was acquired on 1 April, 
1975 at approximately 4:30 in the afternoon and at 11:30 at 
night. Some rain had fallen within the 24-hour period prior 
to the overflights and approximately six inches of rain had 
fallen within the three weeks prior to the mission, thus, the 
soil was wery wet. In spite of this, the imagery contained 
considerable useful geologic information. The afternoon, 
thermal imagery Figure 38, looks similar to aerial photography 
acquired at a low sun angle. Those areas not in direct 
sunlight are cooler and consequently image in darker tones. 
Density slicing of the image into eight gray scale levels 
emphasizes the contrast between targets of slightly different 
temperatures. With the system used, this density slicing is 
keyed to the black body reference temperatures, established at 
the time of data acquisition. Consequently, each gray level 
on the image represents a known range of radiant temperature. 

Figure 39, daytime thermal imagery processed with the 
contour algorithm (see Appendix F for further detail), em- 
phasizes the linear nature of several features. The linear 
labeled W in the upper left corner of Figure 39 is pronounced 
on this image, but it is difficult to see on the eight-level 
processed image and is extremely subtle on the continuous tone 
(analog) print. Detailed examination of the large scale color 
photography lends some support to the presence of a fracture, 
but without the emphasis provided by contouring the analyst 
overlooked the feature. Linear X, prominant on this image as 
on other types of remote sensor data, is interpreted as a 
fault. Linear Y is an extremely straight side of a flatiron 



123 




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of Keefer sandstone, and, consequently, is suspect of being a 
fault. The tip of the flatiron is near Point y, but the 
linear appears to extend beyond the crest of the ridge which 
further supports the hypothesis that it is a fault. Inter- 
pretation of the aerial photography, however, does not indi- 
cate any appreciable displacement across this feature. It 
could represent a prominent fracture and, from an engineering 
point of view, be of concern in tunnel boring. Linear Z is 
less obvious on this image, but is of such length that it 
could intersect the tunnel near the north portal. Numerous 
other linear features visible on this image may be of struc- 
tural significance. It is emphasized, however, that thermal 
imagery should be analyzed in conjunction with aerial photo- 
graphy. This is particularly important with imagery such as 
Figure 39 which has lost most of its "photographic" character. 

The two bands of the thermal imagery. Figures 40A and 
B, acquired during the 11:30 p.m. overflight, look essentially 
identical. The only large rock exposures in the area are of 
the Tuscarora sandstone along the crest of the mountain. Here, 
Point K, Figure 40B, it consists of two massive resistant 
sandstone beds (light toned) separated by a softer shaly sand- 
stone unit (dark toned). The two resistant units appear warmer 
on the imagery because of the high thermal inertia of the sand- 
stone. The Juniata shale and sandstone sequence underlies the 
Tuscarora sandstone. Point L. The upper portion of this unit 
appears darker or cooler than the underlying strata on the scarp 
slope. This may be because the area immediately below the 
Tuscarora escarpment is shaded for a major portion of the day 
and is more sheltered from insolation than other parts of the 
mountain. The scarp slope consists of relatively non-resistant 
rock and the entire slope is covered with a soil mantle of 
varied thickness. The only place the Juniata formation outcrops 
is near the top of the slope where the soil is thinner. The 
difference in the emissivity characteristics of the Juniata 
bedrock exposures and the thin soil cover also may contribute 
to the differences in apparent temperature. 

The dip slope of the East River Mountain is moderately 
dissected with small drainage systems between the flatirons. 
Many of these drainage channels, particularly on the upper 
portion of the mountain. Points M, Figure 40B, are substantially 
lighter in tone, appearing much like the bare rock exposures 
of the Tuscarora sandstone at the crest of the mountain. 
Field examination of several of these drainage systems 
revealed that there are boulder trains composed of large 
blocks of Tuscarora sandstone concentrated in the gulleys. 
Several dark tone features of linear nature can be seen on 
the imagery. Linear, X, in Figure 40B, is identical to "X" 



126 



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on Figure 39 and is the fault identified as F-| on Plate II 
and V (in pocket). On this imagery, it is seen as a faint 
dark line extending from the ridge crest to the south portal 
of the tunnel. Another dark toned linear feature identified 
as Y in both Figures 39 and 40B and as F4 on Plate II and V, 
extends from the tunnel course in a northeasterly direction. 

In this heavily vegetated area, the ground is nearly 
totally covered with a blanket of dead leaves. The area 
around Point P, Figure 40B, has been partially cleared and 
heavily used as a livestock holding area. Considerably more 
bare ground is exposed here than in the adjacent areas. The 
wet ground has been cooled by evaporation, thus, appears as 
dark-toned. The dark zone labeled N is a power line right-of- 
way that has had the vegetation removed and bare ground 
exposed. 

Figure 41, the ratioed image of the two thermal chan- 
nels, shows close similarity in the response of the two 
spectral bands except for two distinct areas. Theoretically, 
areas of high silica content should appear dark on this 
image. The sand quarry at Point T is dark just as theory 
predicts. 

The area, V, a short distance above the south portal 
building appears equally dark on both channels of thermal 
imagery, Figure 40 A and B. These dark tone areas proved to 
be of comparable apparent temperatures and, thus, essentially 
cancelled out on the ratio image. In contrast, the area U in 
front of the south portal appears dark, indicating consid- 
erable silica (quartz sand) within this area. Examination of 
the aerial photography and field observations indicates that 
the area was freshly tilled and probably seeded, but not 
overgrown with grass. The area behind the portal building was 
approximately 50% covered with lespedezaB/ which was appar- 
ently adequate to mask the silica response on the 8-10 ym band 
imagery. 

Sink holes known to be present in the vicinity of the 
north portal are not easily seen on the thermal imagery. This 
is not surprising, as at least one of two factors would need 
to be present for them to stand out on the imagery. First, 
there would need to be a substantial difference in soil mois- 
ture content in the depressions and the surrounding area to 
create a thermal contrast. The excessive rainfalls that 
occurred in this area immediately before the overflights 



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precluded this difference being present. Second, sink holes 
connected to an open underground cavern system may exhale 
warmer air at night which would then warm the soil around the 
opening in the sink hole. The cavern system in the area north 
of the ridge was probably filled with water because no such 
warm spots are identifiable. One or two of the sink holes 
which contain standing water appear on the thermal imagery as 
warmer areas. These, however, could only be identified after 
correlation with aerial photography. 

In summary, the thermal imagery of both the Carl in 
Canyon and the East River Mountain test sites produced new 
information as well as corroborated information from other 
sources. The identification of features on the thermal 
imagery that were originally mapped by other techniques prove 
that these features are real and may be of structural sig- 
nificance and important to engineering decisions. 

All of the stratigraphic units on the dip slope of the 
East River Mountain contain a substantial quantity of silica. 
However, the only place that the ratioed image indicated a 
concentration of silica was in a small borrow pit where fresh 
exposures exist. None of the natural exposures of bedrock 
appear to conform to the theory that silica-rich rocks show 
an emission minima in the 8-10 ym spectral range. Figures 25 
and 42 are ground photographs of the Tuscarora and the Rose 




imi» 



Figure 42 - This outcrop of ferruginous Rose Hill sandstone siiows the typical lichen 
coating prevalent in this area. 



131 



Hill formations and are typical examples of the nature of the 
rock outcrops in this area. In all instances the surface of 
the natural rock exposures are almost completely covered by 
lichens. Because the depth of sensing of thermal imagery is 
only a few micrometers, the lichen cover effectively masks the 
true nature of the rock. 

Based upon the results of the thermal survey at this 
site dual-channel thermal imagery and ratio analyses provides 
little additional information of geological significance in a 
humid environment. Single channel imagery, on the other hand, 
contains substantial information of geological significance. 



7.7.3 Additional Examples of Thermal Imagery 

One might argue that the tunnel sites used in this 
investigation were poor for demonstrating the full capabili- 
ties of thermal remote sensing. However, the sites were 
selected arbitrarily, without bias, except for climatic con- 
ditions, and the sites are typical of most tunnels located in 
similar climatic zones. 

The Carl in Canyon site is a well drained meander spur 
in an area of low rainfall, four inches (10 cm) per year. The 
imagery was acquired after an extended dry period (six-seven 
months). If the faulting would ever have been detectable with 
thermal imagery as a result of differential moisture concen- 
tration along fault traces it would have been shortly after 
the rainy season, i.e., April or May. 

The East River mountain site receives 40-60 inches 
(100-150 cm) of rainfall per year. The test area was over- 
flown as late in the winter season as practical (1 April); 
further delays ran the risk of having a leaf canopy mask the 
ground. This necessitated acquiring the thermal imagery after 
heavy rains (six inches, 15 cm., in the previous three weeks). 
The ground was saturated and differential moisture concen- 
trations along fault zones were minimal. 

Thermal scanning systems are generally considered to 
provide consistently better results for geological analysis in 
arid environments because of better rock exposures and the 
marked effects small moisture differences can have on the 
radiometric temperatures of rocks and soils. It is this 
latter property that can produce unique results with thermal 
scanning not obtainable with shorter wavelength sensing 
systems. 



132 



It is felt that the full potential of thermal infrared 
imagery was not adequately demonstrated in the results of the 
investigation. Thus, additional examples of 8-14 ym imagery 
are included. However, in all honesty, these examples repre- 
sent exceptionally good results and should be judged in that 
context. 

Figures 43 and 44 are examples of thermal imagery and 
black and white panchromatic photography of an area in south- 
western United States. The value of the thermal imagery as a 
complement to conventional photography is obvious. Although 
the thermal image, Figure 43, has not been corrected for scan 
angle distortion, correlation between the two images is not 
difficult. The stratification of the alternating sequence of 
limestone (light tone) and carbonaceous shale (dark tone) on 
the thermal imagery. Points a, b, c, and d are more distinct 
on the thermal image. Faults f-\ and F2 are evident on both 
the photography and the thermal imagery, however, fault F3 
is much less distinct on the photography. The higher tonal 
contrast between the different lithologies as shown on the 
thermal image permits greater reliability in correlation of 
stratigraphy across the fault. 

The value of thermal imagery for locating hidden 
faults under certain conditions is illustrated in Figures 45A 
and 45B. The upper image is a black and white panchromatic 
photograph of a dry desert wash. The lower figure is an 8- 
14 urn thermal image of the same area (the arrows on each image 
will help to correlate the scenes). In the aerial photograph 
there is no visible evidence of faulting. However, in the 
thermal image the dark tone area appears bounded by two 
faults (see arrows) that are upthrown on the lower left and 
the lower right. These faults have formed a barrier to 
groundwater movement and the evaporative cooling effects 
produced by the higher concentration of soil moisture behind 
these barriers have created a temperature differential suffi- 
cient to be detected by the thermal sensor. 

Small scale thermal imagery can be useful where there 
is inadequate information on the regional geology of an area 
of interest. Figure 46 is an example of imagery acquired at 
an altitude of about 25,000 feet (7260 meters) AMT. It shows 
numerous lineaments that can only be explained as faults or 
fractures. 

Thermal imagery, as emphasized above, is sensitive to 
temperature differences produced by small variations in the 
moisture content of soils. Differences in thermal inertia of 
materials can also be a significant indicator of geology. 



133 





B 



Figure 43 - The light and dark toned banding on this 8-1 4um thermal image shows a marked difference in 
thermal response of the limestone (light toned) and the black, carbonaceous, blocky shale. This sharp 
display of the stratigraphy is an aid in mapping faults and fractures as shown in image B. Compare this 
image with Figure 44 which is a panchromatic aerial photograph of the same area. 



134 




Figure 44 - Lithological discrimination on this panchromatic aerial photograph is typical of such photography In 
arid regions. A resistant strata, probably limestone or sandstone, is underlain by strata which appear faintly on 
this photograph as alternating bands of light gray. Anomalous topography and vegetation alignments show several 
faults or fractures present in the area. Compare this image with Figure 43. 



135 




■^ 




B 



Figure 45 - Much of the arid desert area of the Western United States is covered with extensive 
sheets of alluvial and colluvial waste material which disguises much of the structural geology. 
In this matching pair of images of panchromatic photography (image A) and 8-14um thermal 
infrared imagery (image B), the utility of thermal imagery for revealing some of the hidden 
structure is illustrated. The obstruction of the movement of groundwater by faulting is shown by 
the coaler dark toned area. 



136 



Briefly, less compact materials generally have a lower thermal 
inertia than more dense materials. This property combined 
with the effects of soil moisture differences makes the ther- 
mal scanner an effective tool in evaluating an area for po- 
tential landslides. Figure 47 A is an 8-14 m thermal infra- 
red image of an area near Newport Beach, California. This 
imagery was acquired near midnight in November after an 
extended dry season. Figure 47 B is an aerial photograph of 
the same area showing old landslides identified by Vedder (1957) 
The main areas of interest in this photograph are the sides of 
the large elongate hill traversed by the dirt road. The 
letter symbols identify the same areas on both images. The 
majority of the dark tones occur within identified bounds of 
landslides and are interpreted as areas of looser soil com- 
paction and higher concentrations of soil moisture. This 
is indicative of the slide areas that have not completely 
stabilized. Any construction that cuts into these areas would 
probably reactivate movement. Note that some dark toned areas 
lie outside the slide areas suggesting that movement has been 
more extensive than mapped. 




Figure 46 - Small scale thermal Infrared imagery can have utility in geological mapping as is illustrated in this image 
from the Western United States. This image was acquired at an altitude of about 25,000 feet (7,600m) and covers 
a distance of approximately 9 miles (14.5km). It shows several linear features of obvious structural significance 
that do not appear on the state geological map. 



137 





B 



Figure 47. On the 8-l4um thermal infrared image (upper image) of an area near Newport Beach, California, 
acquired after an extended dry period, the dark toned zones are interpreted as cooler because of higher 
concentrations of soil moisture. These areas show a high coincidence with areas mapped as landslides by 
the U. S. Geological Survey. The nrtapped landslide areas are annotated on the aerial photograph in heavy 
black lines with arrows showing direction of movement. The nrraist areas identified from the thermal imagery 
are outlined on the photograph by dotted lines and are letter coded for correlation on the two images. The 
heavy dashed lines show the area of coverage from the thermal scanner mission. 

One can infer from the correlation shown that the soils and bedrock in this area are prone to slumping and 
that, although the slides are presently stabilized, portions could be reactivated by disturbance of the toe of 
the slide or by unusually heavy rainfall. 



138 



7.8 Magnetometer Survey, East River Mountain 

A review of the map in Plate III, the contoured aeromagnetic 
data, shows a magnetic response only to the reinforcing steel in 
the concrete of the East River Mountain tunnel. This map shows a 
linear anomaly along the tunnel path with peaks over each portal as 
expected. The contour interval on this map is 25 gammas, which is 
approximately the minimum allowed by the line spacing and the noise 
level of the data (+ 5 gamma). The outcrop line of the Rose Hill 
formation (a ferruginous Clinton iron formation equivalent) may be 
indicated by a faint eastward bulging of the contours on the south 
slope of East River Mountain; however, this could not be inter- 
preted from contour maps as delivered by the geophysical survey 
subcontractor. 

Because of the possible importance of the Rose Hill Formation 
as a magnetic strati graphic marker-4/ in the structural interpre- 
tation, the original data strips were examined for evidence of 
small anomalies. The geophysical interpretation plate indicates 
the location of minor magnetic peaks that might be correlated with 
a yery v/eak magnetic horizon in the sediments on the south slope of 
East River Mountain. These series of peaks form two northeast 
trending lines, f^ and fg. Figure 48, just west of the south por- 
tal, fg when extended across the fault, f ] , (see Plate V) coin- 
cides with the straight side of a Keefer sandstone flatiron. This 
is interpreted as indicating a possible fault in the section. This 
reinforces the photogeologic interpretation of the physiography and 
suggests that one effect of the fault movement is to move the Rose 
Hill formation up on the southeast relative to the northvyest side 
of the fault. The effect of this movement at tunnel level would be 
to effectively thicken the Rose Hill formation over the expected 
thickness derived from careful measurement of a strati graphic 
section. 

Because of the direction of movement on these northeast 
trending faults which causes a repetition of section across them, 
they are readily defined by the magnetics. The fault shown in a 
north-northwest direction is much more difficult to define magnet- 
ically, perhaps because of the direction of movement, but also 
perhaps because of the direction of the flight lines. 

A magnetic survey of this sort is generally flown with noise 
levels below one gamma. This allows contouring of the data to 
about five gammas. However, the electromagnetic system and the 
magnetic system cross-feed slightly, and to obtain the best pos- 
sible EM signal a slight degradation of the magnetic signal was 
allowed. A five-gamma contour interval would have better defined 
the Rose Hill formation on the contoured aeromagnetic map. 



4/ Magnetic susceptibility tests conducted on Rose Hill samples show 
very weak responses. Measured on cored samples with a bridge 
circuit, the average response was .05 x 10-3cgs/cc. 

139 




/ / 6.- 

^ O '^ 

/ r^o 

o *» 



X 



y 






305 eiOMts. 





Interpreted zone of faulting 
and shearing. 


. Jl 11 


Low resistivity anomaly 


-o- 


Magnetic anomaly. Number 


in gammas above background 


o — o — o 


Power line 



FID'lSg Line 19 '^ 



Figure 48. Geological structure map prepared from the detailed evaluation of airborne magnetic 
and resistivity chart records in conjunction with the analysis of aerial photography. 

140 



An important conclusion from this phase of the project is 
that, in order to obtain maximum benefit from an aeromagnetic 
survey, the data, must be interpreted in conjunction with all 
available geologic data. 



7.9 Airborne Electromagnetic Surveys (AEM) East River Mountain 

The Dighem AEM system provided the data for the contoured 
resistivity map. This map is an apparent resistivity map in the 
sense that the earth was modeled as a uniform conducting half space 
and the resistivities were calculated from the whale tail (see 
Appendix G for a description of the system) coil response based 
upon that assumption. At the frequency of about 900 Hz, the system 
is sensitive to resistivities in a range from 1 to 1,000 ohm-meters 
The resistivity map shows apparent resistivity contours in this 
range, which may be interpreted as the average resistivity from the 
top of the first conducting zone to a depth of about 150 feet 
(45m). 

The contoured apparent resistivity map shows essentially four 
kinds of "anomalous" response, two from cultural features and two 
from near surface geologic features. The first culturally derived 
anomaly is the sharp linear power line anomaly that trends sub- 
parallel to the tunnel (north-northeast) across the survey area. 
This is a major powerline, well balanced and grounded so that the 
reponse is a purely conductive one from the amount of conductive 
metal in the line. There is no response on the 60 Hz monitor or 
the flight line record, but the sharpness of the response on each 
flight line and the linearity of the plan pattern would leave 
little doubt as to its cause even if the powerline structures were 
not visible on the photography. The other culturally derived 
anomaly is manifested over the two portals of the tunnel. These 
anomalies would be suspected upon examination of the photo-mosaic 
because of the surface disturbance shown. They are due to both a 
conductive response and a magnetic response from the maximum con- 
centrations of near surface iron as shown in the magnetic contour 
map. This is apparent in the electromagnetic data strips as a 
negative response in the quadrature (out of phase) output of the 
minimum coupled receiver coil. 

The two responses from geologic sources are both of interest 
in tunnel site investigation. The broad linear northeast trending 
anomaly to the immediate north of the north portal is interpreted 
as an anomalous response from the outcrop band of the Moccasin and 
Eggleston limestones. This limestone sequence has many small sink 
holes along the outcrop. From the conductive response we may 
conclude that these sinkholes and underlying channels are saturated 
with ionized groundwater and that the interconnective "plumbing" of 

141 



the groundwater system is yery good. In other words, an advancing 
tunnel face may encounter water filles cavaties which may affect 
tunneling progress and stability of the opening. 

The second geologic anomaly is located east of the tunnel high 
on the south slope of the East River Mountain. The anomaly is 
nearly circular in plan and is calculated to be 200 feet (61m) deep. 
This anomaly is interpreted as a water saturated fault intersection. 
One of the faults in the northwest trending zone, fy, Figure 48, 
extends just to the northeast of the north portal and is interpreted 
as having a steep westward dip. The other fault zone is interpreted 
from the aeromagnetic data. It is difficult to determine which zone 
offsets which at the point of intersection. They may mutually 
offset each other and such a mechanism may have produced an unusually 
porous, permeable, nearly vertical plunging zone that might cause 
great difficulty in tunneling. It is probable that the zone is both 
unusually broken for the area and that it is saturated with ground 
water. Such a zone would be difficult to detect in this area except 
by the most detailed ground resistivity survey. 

A similar condition may have also existed at the present tunnel 
site. The same sets of faults appear to intersect in the same way 
just above the south portal on East River Mountain, but it is not 
possible to detect it now because, if actually present, the zone 
would have been drained by the tunnel. The ability to detect the 
zone with conductivity measuring devices is dependent upon the 
conductivity of the rock aided by interconnected water zones. It 
should be also noted that this is a local condition of small areal 
extent and avoidable with only very minor realignment of the tunnel. 
The small area covered by most ground resistivity surveys might not 
indicate how localized this condition is and how avoidable it is. 

The unique contributions of the airborne magnetic and electro- 
magnetic data are that they measure directly the response from a 
volume of rock and the inferences involved in the interpretations 
are inferences concerning volume of rock, not simply the surface 
manifestation of subsurface conditions. When interpreted in con- 
junction with all available geologic data, airborne geophysical data 
provide uniquely powerful information about subsurface conditions. 



142 



8.0 THREE-DIMENSIONAL MODELING 

The ultimate goal of a tunnel site investigation is to provide the 
engineer with an understanding of the geologic and engineering conditions 
at tunnel level. This is done by extrapolating geologic conditions 
observed at the surface into the subsurface. These extrapolations are 
supported by basic geologic principles, data from borings, exploratory 
excavations, geophysics and any other subsurface data as available. 
However, there are many limitations and inaccuracies associated with 
both conventional and remote sensing site investigation techniques when 
they are used to predict subsurface conditions. In order to minimize 
the possibility of incorrect conclusions one strives for a convergence 
of evidence provided by using several techniques. Each additional unit 
of information supports and serves as a check on other information. 
With subsurface data acquired using airborne geophysical techniques and 
surface data acquired using airborne remote sensing and field mapping, 
it is possible to construct a three-dimensional geologic model of the 
site. This preliminary mode provides a framework for guiding the col- 
lection and evaluating the results of subsurface and ground geophysical 
studies. 

A three-dimensional geologic model of a tunnel site is an abstrac- 
tion that embodies the arrangement of geological features. In its most 
complete form it would include not only the distribution, geometry, 
attitude, and composition of all of the lithologic entities and features 
that act as discontinuities, but the hydrologic. and engineering proper- 
ties of all materials present as well. It would be prohibitively expen- 
sive and physically impossible to acquire all of the data necessary to 
create this ideal model. In addition, short of using an immense amount 
of computer storage space it would be impossible to represent the model 
in any useful way. However, in practical terms it is possible to 
present the data acquired by remote sensing and conventional methods in 
a variety of ways; one of the most useful is a series of parallel and 
intersecting cross-sections. As the site investigation progresses, 
additional data can be added to the originally chosen cross-sections or 
new cross-sections constructed. 

Beginning with remotely sensed data such a model is constructed 
from a series of cross-sections drawn from topographic maps. The sec- 
tions are selected so that they will intersect significant geologic 
features identified during the data analysis phase. Important features 
for three dimensional modeling are lithological boundaries, stratigraphic 
continuity, faults, joints, and other structure. With photograimetrically 
determined (or field measured) strikes and dips, apparent dips along the 
section can be calculated and a bedding plane or contact can be projected 
from the surface to tunnel level. Similarly, fault planes, offsets 
along these planes, and associated fractures can also be projected to 
tunnel level. 



143 



By constructing a cross-section along the alignment of the proposed 
tunnel the approximate location in the tunnel of specific geologic 
features can be determined. For example, the horizontal extent of a 
certain rock unit in the tunnel can be estimated, the point at which 
fractured rock might be encountered and other features such as sub- 
terranean solution cavities and water can be estimated. This simple 
physical model not only portrays the data in an easily understandable 
form, but can act as a check on the validity of inferences and indicate 
areas or features where further investigations should be concentrated. 



8.1 Carl in Canyon Model 

The geologic analyses of Carl in Canyon made using data collec- 
ted by different remote sensing systems were compiled on black-and- 
white panchromatic photography. A GMB stereoscopic plotter was 
used to produce a topographic map and to transfer the geologic 
interpretations from the photographs to the map. Strike and dip 
measurements were made photogrammetrically, where possible, to 
supplement the field data. These measurements were used to cal- 
culate the apparent dip along the cross-sections drawn for the 
Carl in Canyon site (see Plate II in pocket). 

Where observed, the fault planes were nearly vertical and this 
premise was used throughout model construction. The displacement 
on some of the faults would have been very difficult to determine 
without constructing the model. By studying the contact between 
the Strathearn limestone and the Diamond Peak conglomerate at 
cross-sections D-D' and F-F' , the displacement of the fault F-] on 
cross-section D-D' was determined to be approximately 65 feet (20 
meters). The displacement of the other faults could not be deter- 
mined due to the lack of specific evidence such as stratigraphic 
correlation on opposite sides of the fault. 

From the first version of the model it was apparent that the 
position of a portion of the Diamond Peak - Strathearn contact, 
where it had been inferred, by considering soil and talus cover, 
had to be repositioned. 

Using the model it was possible to estimate the location of 
the faults and the horizontal extent of each rock type in the 
tunnel. The three-dimensional model was important in evaluating 
the validity of the geologic interpretation of this site. 



8.2 East River Mountain Three-Dimensional Model 



Like Carl in Canyon, the geologic analysis at East River Moun- 
tain was based on data from several different remote sensing systems. 

144 



The analyses from 
that was prepared 
photographs were 
was encountered w 
photogeologically 
model . The error 
thicknesses of a 
tion of the three 
but it indicated 
to be made. 



all sensors were compiled on a topographic map 
with a photogrammetric plotter. Natural color 
used to make the stereo plates. Some difficulty 
hen the contact between formations, as mapped 
, were incorporated into the three-dimensional 
in plotting the contacts resulted in inconsistent 
formation without evidence of faulting. Construc- 
-dimensional model not only made the error apparent, 
along which cross-section a re-interpretation had 



Fault F] on Plate I offsets the contact between the Keefer and 
the Rocky Gap formations. The amount of displacement is difficult 
to estimate on the aerial photograph; but using the model the 
displacement could be estimated to be at least 50 feet (15m.). 

Because there are no outcrops of the Juniata and Marti nsburg 
formations at or near the tunnel site it was difficult to locate the 
contact between them. The contact of the Juniata and Marti nsburg 
was drawn based on the thickness of the Juniata estimated in a 
preliminary report by Smith (1968). There is, however, evidence of 
a change in lithology considerably below this approximated contact. 
The evidence is a bench which is most prominent on section C-C on 
the north slope. A dashed line on the profile indicates this stra- 
tigraphic break. Photograimietric plotting of other lithologic 
contacts produced formation thicknesses that correspond reasonably 
well with the thicknesses reported by the tunnel contractor with the 
exception of the Rocky Gap formation (Table 5) which appears sub- 
stantially thicker than reported. 

Table 5 Comparison of Formation Thickness at East River Mountain 







PREVIOUS WORK 






MODEL 


ANALYSIS 






THICKNESS 


TUNNEL 


THICKNESS 


TUNNEL 


FORMATION 


FEET 


METERS 


LENGTH 


FEET 


METERS 


LENGTH 


ROCKY GAP 


25 


8 


50 


15 


210 


64 


250 


76 


KEEFER 


40 


12 


88 


27 


55 


17 


160 


49 


ROSE HILL 


185 


56 


393 


120 


180 


55 


430 


131 


TUSCARORA 


155 


47 


367 


112 


165 


50 


390 


119 


JUNIATA 


320 


97 


690 


210 


320 
(650) 


97 
(198) 


740 
(1400) 


225 
(427) 


MARTINSBURG 


1500+ 


457 


2705 


824 


1600 
(1300) 


488 
(396) 


3150 
(2480) 


960 
(756) 



MOCCASIN 380 116 615 187 

145 



410 



125 



8.3 Limitations of the Three- Dimensional Model 

The description of surface features using remote sensing 
systems and three-dimensional modeling of these features at tunnel 
depth is a useful combination of techniques for predicting condi- 
tions to be encountered during tunneling. However, this combina- 
tion cannot totally eliminate the need for actual subsurface measure- 
ment, seismic surveys, boring or excavation. Remote sensing and 
modeling can greatly reduce the quantity of subsurface measurements 
required by indicating where the information is needed. 

To summarize, three-dimensional modeling of the geologic 
conditions at a proposed tunnel site is a valuable tool for the 
design and construction engineer. Surface data, acquired by remote 
sensing methods, combined with subsurface data, the acquisition 
of which is directed by prior surface data analysis, can be used to 
produce an accurate assessment of many conditions along the tunnel 
route. Three-dimensional models not only present geologic data in 
an easily understood form, they can point out errors of interpreta- 
tion, indicate areas that require further investigation, and guide 
the collection of subsequent data. 



146 



9.0 ECONOMIC ANALYSIS OF REMOTE SENSING AND CONVENTIONAL SITE 
INVESTIGATION TECHNIQUES 

9.1 Introduction 

A tunnel site investigation is planned and executed on the 
basis of incomplete information about the site geology and frag- 
mentary information about the eventual tunnel design, method of 
construction and construction cost. The investigator is, therefore, 
at a disadvantage when he makes his decisions with respect to the 
quality, quantity, and the methods for most efficiently obtaining 
the geologic information required for the project. 

The problem of planning a tunnel site investigation could be 
routinely handled if the relationship between investigation cost 
and construction cost savings were fixed or could be defined through 
economic analysis. The cost effectiveness of each increment of the 
investigation, however, is difficult to define in practice because 
the cost of both the investigation and the construction are affected 
by site conditions and the characteristics of the tunnel project. 
The quantity and quality of geologic information obtained by a 
specific method, for instance, varies with environmental conditions 
and the site geology. The value of the geologic information in 
turn varies with the tunnel design, the method of construction, the 
character of the construction plans and specifications, and the 
efficiency of the contractor's operations. The investigator can 
normally expect to have only a crude basis for evaluating the cost 
effectiveness of alternative investigation methods. 

Fortunately, most investigation methods involve a relatively 
small investment when contrasted with the cost of tunnel construc- 
tion. On most projects the cost of the entire site investigation is 
less than 1% of the cost of construction. The cost of difficulties 
resulting from incomplete geologic information, on the other hand, 
may be many times greater than the cost of the investigation. The 
investigator, therefore, can normally assume that a method which 
offers some possibility of providing additional geologic information 
will be cost effective. 

The goal of the investigation plan is to locate and measure 
the geologic features which will affect tunnel design and construc- 
tion. Whether conventional or remote sensing techniques, the 
methods selected for the work and the extent to which each method 
is used depends on the investigator's appraisal of the capabilities 
of alternative investigative methods available, the level of 
accuracy required for the proposed construction, and the limitations 
imposed by the investigation budget. Some geologic features may be 
satisfactorily investigated by a single method because of either 
the high capability of the method or low accuracy requirements, or 
both. In other instances, two or more methods are required to 
investigate a single class of geologic features. 

147 



It is obvious that unit investigation costs and environment- 
dependent capabilities of a sensor cannot be definitively stated. 
In addition to these problems, there is no specific remote sensing 
experience base in tunnel activities from which to derive empirical 
cost data. In this analysis the data assumptions, cost estimates, 
and results are made as explicit as possible, but it is important 
that both analysts and decision makers who will use these results 
recognize the potential error that they may introduce without 
careful consideration of the variables for each specific project. 

This section is addressed to the investigator who is faced 
with a problem of designing a tunnel site investigation program 
comprising both conventional and remote sensing methods. From the 
material presented, he will become familiar with the capabilities 
of various conventional and remote sensing systems. The range of 
costs presented are averages based on the experience of the authors. 
With this information the investigator will be able to design a 
multi-stage route and site investigation program while considering 
the variables and conditions of his specific project. 



9.2 Conventional Means of Data Collection 

The following is a brief description of the methods currently 
used in tunnel site investigations and a discussion of the advantages, 
limitations, and costs associated with each method. Table 6 summa- 
rizes the major points presented in the chapter. 



9.2.1 Information Search 

A tunnel site investigation normally starts with a 
file and library search to obtain pertinent geologic and 
construction information. Publications of federal and state 
geological surveys and other government organizations such as 
the U.S. Bureau of Reclamation, Corps of Engineers, or Soil 
Conservation Service often contain information about the soil, 
bedrock and groundwater conditions of the site. This infor- 
mation may be supplemented by geology thesis studies on file 
in local college libraries, consulting engineering files, logs 
of local well drillers and other records of building, pipeline, 
highway and tunnel construction. 

Most of this information is available free of charge or 
for a nominal fee. The greatest investment is generally the 
time to collect and review a wide range of reports and records. 
It is very unusual to find sufficient information from these 
sources to completely define the subsurface conditions of a 
tunnel site because the information is usually collected for 

148 



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150 



an entirely different purpose and the geologic observations 
are generally limited to the ground surface. Although most of 
the information is of limited value to a tunnel investigation, 
a careful information search usually reveals enough pertinent 
information to make the search of value on most projects. In 
some instances the information search reveals conditions which 
might have been overlooked in field studies or discovered only 
by the use of expensive field investigation methods. 

The cost of the information search depends upon the 
character, volume and availability of pertinent records. 
Normally the information search will cost from $1,000 to 
$10,000. 



9.2.2 Aerial Photograph Interpretation 

Aerial photographs are commonly used during the early 
stage of a tunnel site investigation to identify exposures of 
bedrock, to delineate major bedrock structures, and to identify 
pertinent geologic features and the presence or absence of 
ground water and surface water. The results of aerial photo- 
graph interpretation are generally considered tentative until 
checked by surface and subsurface investigation. 

Aerial photographs of most sites are available from 
governmental agencies and industrial sources at a nominal 
cost. The site may be photographed for the tunnel investiga- 
tion to obtain more complete or updated coverage. The expense 
of this work is usually moderate compared with other investiga- 
tion methods and the new photographs are normally required for 
both geologic and topographic phases of the investigation. 
The cost of interpretation of the aerial photographs is 
nominal . 



9.2.3 Surface Mapping 

Surface mapping is the classical method of obtaining 
information about subsurface conditions. Surface mapping 
involves the inspection and recording of soil, bedrock, and 
water conditions exposed in cliffs and stream beds and in man- 
made excavations for buildings and highways. Supplemental 
bedrock exposures may be obtained by use of hand or portable 
powered equipment. Surface mapping provides a two dimensional 
view of the geology. This information is projected to the 
depth of the proposed tunnel to obtain a three-dimensional 
picture of the site conditions. 



151 



The reliability of surface mapping to identify the i 
significant geologic features depends on both the geologic ' 
conditions and the nature of proposed project. The reliability 
of the geologic projections depends upon the extent of surface 
exposures, the nature of the geologic units, the complexity of ; 
the geologic structure and the continuity of the surface and 
subsurface features. The degree to which tunnel construction 
will be effected by variations in the geologic conditions 
depends upon the depth of the tunnel, the tunnel bore diameter, 
and the method of excavation and support of the ground to be ■ 
used during tunnel construction. ,, 

Reliable projections of ground conditions can be expected 
for a tunnel alignment at moderate depth in massive, well- 
exposed granitic rock. The reliability of surface projections ■ 
is less in terrains underlain by bedrock with a complex geo- j 
logic structure. The reliability may also be low in terrain j 
underlain by alternating competent and incompetent sedimentary 
rocks because the incompetent rock may be poorly exposed or 
completely obscured by soil deposits. For shallow tunnels in 
glaciated terrain, ground condition predictions based solely ' 
on surface mapping can be dangerous because the depth to ,i 
bedrock and the condition of the bedrock along the tunnel I 
alignment may not be evident in surface exposures. J 

{ 

Despite these limitations, surface mapping is a normal 
and useful part of a tunnel site investigation. Surface 
mapping is normally performed because it provides direct 
evidence of the character of the ground and usually provides a 
basis for planning the more expensive subsurface investigations. 
The cost of surface mapping varies with the extent of surface 
exposures and the difficulty of access to various parts of the 
site but should be on the order of $100 to $400 per square 
mi 1 e . 



9.2.4 Surface Geophysical Surveys 

Surface geophysical surveys have been used on tunnel 
sites to locate groundwater levels, determine depth-to-bedrock, 
to estimate excavation characteristics of soil and rock and to 
locate weak or incompetent zones within the bedrock. Seismic 
and electrical resistivity surveys are the geophysical methods 
most commonly used in tunnel investigations but gravity and 
magnetic surveys have application in certain terrains. Most 
surface geophysical testing is performed in the vicinity of 
proposed portal sites. 



152 



i 



Seismic surveys are based upon the principle that shock 
waves, created by mechanical vibrations or blasting, travel 
through different rock materials at different velocities and 
are reflected and refracted in accordance with the basic laws 
of optics. Under these conditions, the travel time between 
the energy source of the shock wave and the seismometer or 
geophone detectors can be used to calculate both the propogation 
velocity through subsurface materials and the depth to the 
interface between materials with contrasting velocities. A 
general knowledge of the subsurface materials provides a basis 
for converting the resulting velocity profile into a generalized 
geologic profile. 

Electrical resistivity surveys are based on the principle 
that the conductivity of earth materials varies with the 
nature of the material and the nature of the contained fluids. 
Resistivity surveys are made by either measuring the natural 
ground currents or by measuring artificially induced currents 
between two or more electrodes at a known spacing. The scale 
of the test and the depth of the investigation can be varied 
by changing the distance between the electrodes. A series of 
measurements can provide a resistivity profile which in turn 
can be converted into a generalized geologic profile. 

The assignment of material type and material properties 
to the velocity or resistance measurements is the most criti- 
cal step of the survey. If the analyst has a good knowledge 
of the local geologic conditions, and rock material properties, 
and if these conditions are relatively simple, the resulting 
geologic profile will be reliable. However, if the subsurface 
conditions are complex, the geologic profile could be less 
accurate. Because of these limitations, surface geophysical 
surveys are used to define the general trend of subsurface 
conditions and the survey results are normally verified by 
borings or other excavations. 

The cost of a surface geophysical survey varies with 
the accessibility of the test site and the required density of 
measurements. A cost of $500 to $10,000 per mile of traverse 
is normal for this work. 



9.2.5 Soil and Rock Borings 

Borings ranging from 1 inch (2.5 cm) to more than 1 foot 
(30.5 cm) in diameter provide samples of subsurface materials 
at depths ranging from a few tens of feet to more than 1000 
feet (305 meters). Most soil borings are three to five inches 
(7.5 to 12.7 cm) in diameter and are advanced by alternately 
drilling and sampling. Core borings in bedrock are generally 

153 



two to three inches (5 to 7.5 cm) in diameter and are sampled 
continuously. The samples and a log of observations made 
during the drilling operation provide a valuable indication of 
the nature of subsurface soil, rock and groundwater conditions. 
This record may be supplemented by borehole logging techniques 
described in the following section. 

Although borings are generally considered the most 
important technique now available for subsurface exploration, 
they have many limitations. Some of these limitations are: 

1. The samples are small with respect to the size of 
the tunnel. In soil this may not be an important 
limitation as a small sample can be representative 
of the soil mass. In rock, the core sample is 
generally not representative of the rock mass because 
the rock mass behavior is controlled by a system of 
fractures which are imperfectly represented in the 
core sample. 

2. Borings are relatively expensive particularly if 
access to the drilling site is difficult, the drill- 
ing conditions are difficult, and the depth to 
tunnel level is great. 

3. Rock and soil samples provide essentially a one- 
dimensional view of the subsurface soil or rock 
mass. Features immediately outside the limits of 
the boring are unknown. In some situations it is 
considerably more difficult to visualize the three- 
dimensional environment of the tunnel from core 
samples than to visualize the same environment from 
two-dimensional outcrop observations. 

4. Core samples are generally not oriented. If core 
recovery is relatively good it is possible to measure 
the dip of geologic features such as bedding, joints 
and faults but the strike of these features is 
unknown unless special oriented drilling techniques 
are employed. 

5. The softer and less competent materials are commonly 
lost during the drilling and sampling. While the 
character of these materials is often critical to 
the evaluation of subsurface conditions, the samples 
merely indicate that the material lost in the samp- 
ling operation were less competent than the recovered 
material. 



154 



The cost of soil and rock borings varies with the size 
and depth of the boring and the surface and subsurface condi- 
tions at the drilling site. A soil boring less than 100 feet 
(30 meters) deep can be expected to cost from $10 to $20 per 
linear foot while a rock boring less than 500 feet (150 meters) 
deep can be expected to cost from $15 to $30 per linear foot. 



9.2.6 Borehole Logging 

In recent years downhole logging techniques, originally 
developed for logging oil wells, have been adapted for use in 
soil and rock borings on engineering projects. The techniques 
include electrical resistivity, sonic velocity, radioactivity, 
gravity, temperature and caliper logs. In the same period, 
devices have been developed for taking photographs or tele- 
vision pictures of small -diameter borings. 

Geophysical well logging has been successfully used in 
the petroleum industry because oil wells are sampled by cut- 
tings and limited cored intervals and the reservoir character- 
istics of oil-bearing strata can be assessed by geophysical 
measurements. The application of geophysical logging to 
tunnel site investigations is less certain because the investi- 
gator is more interested in the stability of the rock mass 
than the permeability of the rock mass. Application of these 
logging techniques should be viewed as experimental at this 
time but these logging devices may be useful in logging deep, 
partially cored borings. 

Photographic logging of borings has been more widely 
accepted because borehole photographs directly supplement 
borehole records and samples. Borehole photographs can be 
used, for instance, to orient each feature noted in the core 
samples and might be used in place of coring to document the 
rock conditions in a boring. Under favorable conditions, 
borehole photography can be used to identify materials in 
zones of core loss. 

Both geophysical and photographic logging are limited 
by borehole conditions. Caving and blockages in the completed 
boring may prevent a complete logging of the hole and, in some 
instances, may result in the loss of an expensive borehole 
probe. Although geophysical logging methods provide informa- 
tion about the rock around the boring, the depth of penetra- 
tion is usually on the order of a few inches or a few feet. 
Even with geophysical measurements, the borehole is still 
essentially a one-dimensional probe of subsurface conditions. 



155 



Geophysical and photographic logging are generally 
performed by well logging service companies. The cost of this 
service is presently dominated by the charge for mobilizing 
and demobilizing the equipment and crews. While the time on 
site may be just a few hours, the cost of making two logs in a 
500 foot deep boring can be $400 to $800. The unit cost of 
the service decreases with an increase in the footage logged 
but the cost increases with the number of logs performed in 
each borehole. 



9.2.7 Exploratory Excavations 

Adits and shafts are occasionally used to explore 
ground conditions in portal areas and in fault zones and 
permeable zones along the tunnel alignment. These excavations 
normally have the smallest cross section which can be con- 
veniently excavated by hand and small power equipment. In 
most instances these excavations extend a few tens to several 
hundred feet from the ground surface. These openings provide 
an opportunity to observe and test the ground conditions which 
is generally not available until construction of the full-size 
tunnel. These openings are carefully mapped in all instances 
and may be used for large scale pumping tests and tests which 
measure the compressibility or strength of the ground. 

Exploratory excavations are relatively expensive, 
ranging from $400 to $700 per linear foot. The excavation and 
support of these openings usually cost nearly as much as the 
excavating and lining of the full-size tunnel because mobili- 
zation costs are distributed over a relatively short length of 
excavation and the work is less mechanized than the work in a 
full-size tunnel. Cost is probably the main reason why these 
excavations are used only in areas where known or suspected 
ground conditions may have a major influence on the design of 
the project and the cost of construction. 



9.2.8 Laboratory Testing 

Laboratory testing is performed on soil and rock 
specimens to measure the engineering properties of earth 
materials and to measure other properties which may be cor- 
related with the engineering properties. The soil tests 
include water content, unit weight, Atterberg limits, uncon- 
fined compressive strength, and triaxial testing. The tests 
on rock include unit weight, water content, abrasion resistance, 
hardness, tensile strength, unconfined compressive strength 
and triaxial testing. 

156 



The basic engineering properties of soil and rock are 
strength, compressibility and permeability. Tests on repre- 
sentative soil specimens can provide the essential information 
to analyze the behavior of soil masses in a tunnel. Tests on 
representative specimens of intact rock, on the other hand, do 
not directly measure the engineering properties of the rock 
mass because rock mass behavior is largely controlled by 
discontinuities. The behavior of a rock mass is assessed by 
comparing the laboratory test results and the field exploration 
information with theoretical models of rock behavior or 
previous tunnel observations in similar materials. 



9.3 Effectiveness and Cost of Remote Sensing Systems 

A discussion of the capabilities of an information gathering 
system must precede any estimate of the effectiveness of that 
system. The optimum capability of each airborne sensor depends on 
several factors which include: cloud cover, season (with respect 
to solar elevation and azimuth, snow and ice conditions, and pheno- 
logical changes of vegetation), soil moisture, depth to bedrock, 
altitude of imaging platform, vegetation cover, cultural inter- 
ference and quality of data processing. 

The capabilities of sensors often overlap, but even though two 
different sensors can identify the same feature, the level of 
detail may be quite different. Overlapping capabilities and dupli- 
cate data can be limited, but it is often helpful to have duplication 
and verification of information. 

The costs for data acquisition using different sensors are 
difficult to estimate. Costs for acquiring the same data can vary 
widely from site to site, and therefore, it is not common practice 
for flying survey companies to quote unit prices. In addition it 
is most efficient to use a single aircraft to acquire several types 
of data making it difficult to partition the cost of the aircraft 
among the several sensors flown. Table 7 lists factors and special 
requirements that control the cost of acquiring certain types of 
data. Table 8 is a summary of remote sensing investigation tech- 
niques, their applications, limitations, and costs. 

Five basic types of remote sensing data evaluated during this 
investigation were data from; 



Satellite imagery 
SLAR (Side Looking Airborne Radar) 
Camera systems (various film types) 
Scanner systems (mul ti spectral , thermal) 
Airborne geophysical systems 



157 



Table 7 Factors Controlling Cost of Remote Sensing Data Acquisition 



Factors 



Elements 



Data acquisition 

Film and processing or 
recording medium 

Data processing 



Field crew 
Equipment rental 

Special equipment purchase 
Mobilization and demobilization 



Stand-by (non- surveying time 
on site) 

Repeat flying 



Special requirements 



Labor 

Type of film, special processing 
requirements 

Computer enhancement, special 
photo lab processing, stereo- 
scopic plotting 

Number, level of training 

Type of equipment, amount of time 
needed, operator 



Accessibility of the site, travel 
cost to and from site and per 
diem 

Size of contract, season, geo- 
graphic location of site 

Equipment malfunction, weather, 
errors (pilot, operator), data 
unacceptable to client 

Specific time of day, weather, 
special reports 



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161 



From the users standpoint, most of the cost factors listed in 
Table 5 do not apply to the cost of data acquired from orbital 
platforms. Standard data are available for a single unit price 
regardless of the geographic location of the site or season of 
acquisition. Likewise if data from other remote sensing systems 
exist, it is possible that it also may be available for purchase at 
some nominal unit cost. The cost information in this section is 
based on costs actually incurred during the study at the two specific 
test sites. 



9.3.1 Satellite Data 

The two types of data acquired from orbital satellites 
used in this study were LANDSAT and SKYLAB imagery. LANDSAT 
(formerly known as ERTS) is a sun synchronous satellite with a 
four channel multispectral scanning system whose bandwidth 
ranges from .5-l.lym. An S-190A multispectral camera and an 
S-190B high resolution camera acquired the SKYLAB data. Color 
and black-and-white images are available or can be recon- 
structed from both systems. 

The spatial resolution of LANDSAT imagery is approxi- 
mately 80 meters, however identification of linear features 
less than one tenth that width is sometimes possible if image 
contrasts are extreme. Scales best suited for geologic 
interpretation are 1:500,000, and 1:250,000. Band 7 (.8- 
1.1 lam) on LANDSAT imagery gives the best information on geo- 
logic structure and topographic landforms. This is not to say 
that other bands should be ignored. Bands 5 and 6 imagery are 
capable of providing good terrain detail. Band 4 imagery, 
however, is often hazy, depending on atmospheric conditions. 

The most outstanding advantage of LANDSAT imagery is 
provided by the broad synoptic view. This is important to 
tunnel site investigation in that regional geologic trends can 
be related to a specific site. Many tunnel sites are selected 
without considering regional geologic trends because there are 
other factors that bear a more inmediate impact on the site 
selected. Some of the factors that control site selection 
include: 

The orientation of existing highways or railroads 

Economic factors (labor, materials cost) 

Site restrictions due to population concentrations 

Facilities which cannot be relocated 

Local geologic parameters. 



162 



These factors, more often than not, claim a higher priority in 
site selection than regional geology even though some elements 
of the regional geology may directly and significantly affect 
the cost and safety of a tunnel. 

In addition to the synoptic coverage of LANDSAT, there 
are several other areas of utility which are of great importance 
to tunneling. They include: the identification of linear 
features often indicative of the fracturing (faults and joints) 
of the rock, identification of drainage patterns, information 
regarding soil types, and rock types and their resistance to 
erosion. 

The cost per frame of LANDSAT is nominal. Black and 
white and color imagery costs approximately $75 at a scale of 
1:250,000. The EROS Data Center price list of LANDSAT and 
SKYLAB data appears in Appendix I. 

The utility of SKYLAB imagery are similar to that of 
ERTS imagery. The SKYLAB camera system has a greater spatial 
resolution (approximately 20 meters) and therefore permits more 
detailed mapping of the regional geology at a scale of 1:250,000- 
1 :125,000 and even 1 :50,000. 



9.3.2 Side Looking Airborne Radar (SLAR) 

An important capability of SLAR is that it provides 
synoptic, relatively high resolution, high contrast images, 
that are useful for interpreting geomorphology and structural 
geology. SLAR is an active system (emits its own energy) that 
can operate day or night regardless of most weather. 

Radar emits pulses of microwave energy directed toward 
the ground and records the energy the ground reflects back to 
the antenna. Areas shielded by topography from incident radar \ 
energy of course do not reflect and therefore appear black on j 

the image. Acquisition of SLAR imagery does not depend on i 

solar illumination and the energy penetrates most clouds; I 

therefore it is not dependent upon time of day or weather , 

conditions. Because the system is independent of solar illu- I 

mination, any side of a topographic landform can be "illumi- 
nated" or shadowed by radar impulses if different flight lines | 
are used. The angle of illumination on most SLAR units can be l 
adjusted to enhance low and high topographic features. ' 

The cost of conducting a SLAR survey for tunnel site l 

investigations is high. The cost could range from $30,000 to I 

$100,000. Alternatively, one could purchase SLAR imagery from 
previous missions, either commercial or military. The U.S. Air 

163 ^ 



Force has acquired SLAR imagery over approximately 70% of the 
United States; the existing imagery is available for $20-$100 
per image. Some parts of the United States have been flown 
commercially and high quality imagery is available (see 
Appendix H). 



9.3.3 Airborne Camera Systems 

The cost of airphoto surveys depends on the type of 
film and camera system used. Color film costs are three to 
four times more than black-and-white film, and the processing 
of color film is about three times the amount of black-and- 
white film. However, this is not to say that the acquisition 
of color photography is three times more expensive than acqui- 
sition of black-and-white photographs. Several other factors 
common to the use of both film types contribute to the cost. 
These include aircraft rental, salaries of pilot and cameraman, 
and reflight and standby factor costs. Color photos can be 
obtained for approximately $2,000-6,000, depending on the 
location of the area, whereas, black-and-white photography can 
be obtained for approximately $2,000-4,000. 

Low sun angle photography (LSAP) sometimes referred to 
as simulated radar, can provide geological information on a 
local and regional scale. The versatility of LSAP is somewhat 
limited by the relatively small range of shadow aspects pro- 
vided by the morning and evening sun through the seasons. 
Different shadow aspects occur at different times of the year 
and the angle of illumination depends on the time of day that 
the imagery is acquired. The advantage of varying the illumi- 
nation angle is that shadow length can be adjusted according 
to local topography. The lower the local topographic relief 
of the area, the lower the sun angle needed to highlight 
topographic features. An area of high topographic relief will 
require a higher solar elevation. 

Black-and-white panchromatic photography provides 
better spatial resolution than can be obtained with color 
film, and the processing of such film also is more economical. 
Panchromatic photography can provide detailed information 
relating to the geologic structure of the area, topography, 
hydrology, vegetation and in some instances, soil types. The 
spatial resolution and geometric fidelity of panchromatic 
photography makes it well suited for stereo-plotting of geo- 
logic information using photogrammetric instrumentation. 

Although the spatial resolution of color photography is 
somewhat less than that of black-and-white photography, the 
human eye can separate more than 100 times more color com- 
binations (hues, values, chromas) than gray values (Evans, 

164 



1948). The identification of many rock, soil, and vegetation 
types depends on subtle color discriminations, thus, color 
aerial photographs are valuable for tunnel site investigations. 

Color infrared photography is excellent for identifying 
vegetation type, vigor, and stage of phenological development. 
Vegetation analysis can be important to tunnel site investiga- 
tions where rock outcrops do not exist, especially if geo- 
botanical indicators exist that can indirectly help to identify 
soil type and soil moisture differences. Color infrared 
photography also can be useful for locating moist fracture 
zones as well as standing and flowing water bodies. 

Generally speaking, color infrared film has a higher 
contrast than standard color film and making proper exposures 
is more critical. It may be necessary to re- fly the imagery 
if the exposure is not correct; particularly if overexposed. 
In most areas color infrared photography is not as useful as 
natural color for geologic analysis. The false color imparted 
to surface features increases the chances for mistaken soil or 
lithologic identification. In general, conditions necessary 
to obtain the optimum performance of color infrared film are 
a certain degree of soil moisture, vegetation in the non- 
dormant state, and as little cloud cover as possible. 

Multiband photos are used to discriminate between soil 
and rock types based on their spectral differences. Multiband 
photos are obtained using panchromatic film, and a series of 
spectrally calibrated filters. By assigning primary colors to 
photo transparencies in the appropriate spectral range, and 
superimposing the photos, a wide variety of false colors and 
near true-color photos can be created. By accenting and 
subduing colors, the spectral differences between rocks and 
soils can be enhanced. 



9.3.4 Scanning Systems (Mul ti spectral , Thermal) 

Multispectral scanners record energy emitted in ranges 
within the visible and near-visible portion of the electro- 
magnetic spectrum. With varied limits all materials have 
characteristic spectral signatures which can be used to dis- 
criminate one object from another. In some areas it is pos- 
sible to identify the different rock and soil types based on 
their relative reflectivity in different bands of the spectrum. 

Optimum performance of a multispectral scanning system 
for geological analysis depends on certain factors: 



165 



• Rock and soil surfaces must be partially free of 
vegetation (trees, shrubs, lichen) 

• Unequal illumination (due to clouds or shadows) of 
the subject should be avoided. 

Multi spectral scanners are commercially available with 
as many as 11 separate channels, ranging from .38-l.lym. The 
data are recorded on magnetic tape which provides the flexibil- 
ity of generating either a direct image or a computer-enhanced 
image in hard copy format. Computer processing the data can 
greatly expand the interpretability of the scanner imagery. 
Many geologic and hydrologic features which are obscured by 
the detail of the original image may be selectively enhanced 
by proper data processing. 

If the geology of the area is complex enough to warrant 
the expenditure, and the proper environmental conditions 
exist, multispectral scanning data can be valuable. If near 
optimum conditions do not exist, cost versus effectiveness is 
greatly reduced. Acquisition of multispectral scanner data, 
computer processing and interpretation of the imagery should 
range from $10,000 to $20,000 per site (cost factors in Table 
7 included). 

While conducting a multispectral scanner survey over a 
site, it is usual practice to acquire thermal infrared data 
using the same scanner system. Because thermal emissivity is 
related in part to the composition of an object, thermal 
mapping can be used to identify differences in lithology and 
soil. Thermal scanners are also useful for mapping fault 
zones by detecting the differences in soil moisture between 
the fault zone and the surrounding area. Thermal scanner data 
can be computer processed using the same algorithms as used 
for multispectral scanner data. 

Thermal imagery is \/ery sensitive to differences in 
soil moisture, and, consequently, is an excellent tool for 
detecting and locating springs and seeps, potential landslides, 
and hydrologic hazards in general. Thermal surveys cannot be 
fully effective if they are conducted when the ground is 
extremely wet. The soil moisture tends to reduce or mask 
emissivity differences between objects and this produces 
a low-contrast image. The addition of a thermal survey to a 
multispectral survey would represent an increase in cost of 
approximately 20% (or $2,000 to $4,000). 



166 



9.3.5 Airborne Geophysical Systems 

Airborne geophysical systems offer the only airborne 
method of directly detecting geological conditions significantly 
below the ground surface. 

Airborne electromagnetic (AEM) systems detect differences 
in resistivity in near surface (0-200 feet; 61 m) rock and 
soils. Thus, these data can indicate the presence of water 
saturated alluvial and coUuvial deposits, mineralized or 
saturated shear zones, basalt dikes and water filled cavernous 
limestone. The Dighem dipole-dipole system used during this 
study can indicate the subsurface orientation of planar features, 
such as fault zones and serpentine bodies, making it unique 
among the sensors tested. 

Aeromagnetic data are a valuable complement to AEM 
data. Airborne magnetometers sense differences in the magnetic 
susceptibility of subsurface soil and rocks, thus, allowing 
for the discrimination of magnetite bearing rocks and for the 
recognition of major discontinuities. This makes it possible 
in some situations to infer the displacement of lithologic 
units across faults. The rather gross resolution of aero- 
magnetic data and the cost suggest that over most tunnel sites 
an aeromagnetometer should not be flown alone. However, the 
additional cost of aeromagnetic data acquisition is small if 
they are acquired at the same time as AEM data. 

The cost of acquiring airborne geophysical data is 
relatively large - $20,000 to $35,000 per site for AEM. 
Aeromagnetic data acquired at the same time might add $1,000 
to the survey costs. However, in many geologic situations 
these data are Invaluable, particularly if faulting and water 
problems are anticipated. 



9.4 Appraisal of Combined Conventional and Remote Sensing 
Investigation Systems 

The goal of a tunnel site investigation is to collect an 
adequate body of geologic information to form the basis for an 
accurate assessment of pre-construction tunneling conditions. This 
goal may be easy or difficult to attain depending upon the surface 
and subsurface conditions, the characteristics of the proposed 
tunnel, and the time or funding limitations of the investigation. 
The many tunnels constructed without major difficulty indicate that 
current Investigations, using two or more conventional methods to 
provide geologic Information, are at least partially successful. 
Many of the tunneling problems that do arise are the result of 
encountering an unforeseen geologic "weak link" such as a fault 

167 



zone, an altered zone or areas of high groundwater inflows. The 
failure of the conventional investigation system to identify a 
critical geologic feature may be the result of limitations of the 
methods of investigation or interpretation used, the investigation 
system, or time and funding available for the investigation. 

In current practice, a tunnel site investigation will almost 
always include an interpretation of aerial photographs, surface 
geological mapping, and borings. Surface geophysical testing is 
sometimes used in critical areas such as portals and low-cover 
reaches of a proposed tunnel. The variety of logging methods 
available are seldom employed in the boreholes produced. With the 
exception of small scale permeability tests in the exploratory 
borings, field testing is rarely used unless there is a possibility 
that the information from the tests will affect design decisions 
and result in major construction cost savings. Some laboratory 
testing of boring samples and outcrop samples is a normal part of 
the investigation. 

The confidence placed in the boring samples may range from 
high to yery low depending upon the uniformity of the geological 
conditions, the skill with which the borings are sited, and the 
recovery of cores and cuttings. 

The end product of a typical tunnel site investigation using 
conventional methods is normally an incomplete picture of the 
surface conditions and inferences about the subsurface supported by 
a few spot checks. Surficial geology may be well exposed in a 
rocky, desert environment permitting accurate and comprehensive 
geologic mapping and photo interpretation, but in a temperate 
environment the ground surface is generally poorly exposed because 
of soil and vegetation cover. 

There are many instances where an analysis of remote sensing 
imagery can make an important contribution to the tunnel site 
investigation. Some examples observed during previous work in 
remote, sensing and during this investigation are; 

I. Identification or differentiation of lithologic units 

a. Identification of rock units over large areas prior to 
surface mapping 

b. Rock unit identification on remote outcrops 

c. Rock unit identification determined from residual soil 



168 



II. Alteration and weathering 

a. Indications of hydrothermal alteration 

b. Depth of weathering, depth of alluvial or colluvial 
deposits, depth to bedrock 

III. Discontinuities 

(Discontinuities are one of the most common problems in rock 
tunnels.) 

a. Trace major fault zones under overburden 

b. Define major joint and bedding trends which are difficult 
to identify because of deep weathering or limited exposure 

IV. Structure 

a. Regional mapping to define regional structural pattern 

b. Locate and delineate concealed structures 

c. Help to define partially exposed complex structures 

d. Measure the attitude of planar entities (beds, fractures, 
etc.) 

V. Groundwater 

a. Identify seasonal changes in hydrology 

b. Identify springs and high water table 

VI. Temperature 

a. Identify high ground temperature areas 

VII. Earthquakes 

a. Topographic evidence of recent earthquakes 

b. Thermally active areas 

Examples of conditions for which remote sensing can be expected 
to be less satisfactory than conventional methods are: 

169 



I. Rock Type Identification 

a. Identification of rock type in areas where exposures are 
abundant and previous field mapping provide at least 
general geologic information 

b. Identification of rock composition in absence of field 
data 



II. Alteration 

a. Areas with deep residual weathering 

b. Areas with deep hydrothermal alteration 

III. Discontinuities 

a. Subsurface location of non-planar major discontinuities 

b. Location and orientation of small-scale discontinuities 

IV. Groundwater 

a. Location of deep water tables 

b. Distinguishing between artesian and non-artesian con- 
ditions where the piezometric surface is below the ground 
surface 

V. Stresses 

a. Location of high horizontal zones 

VI. Natural Gas 

a. Location of gas saturated zones 

Table 9 presents an assessment of the capability of the 
conventional and remote sensing methods to identify, locate, and 
measure significant geologic features under optimum conditions. 
The significant geologic features, which are described in Section 
4.2, are those features which most affect tunnel design and con- 
struction. The capability ratings range from "0", indicating no 
useful information to "5", indicating a high capability to precisely 
locate and measure the geologic feature. 

170 



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171 



= method provides no useful information about the feature. 

1 = method provides an indication that the feature may be 

present (detection). 

2 = method provides a reliable indication that the feature is 

present. 

3 = method provides information to precisely locate the 

feature at one or more locations and provides general 
information about the extent of the feature (identifica- 
tion) . 

4 = method provides information to precisely locate the 

feature and generally assess the properties of the 
feature (analysis). 

5 = method provides information to precisely locate the 

feature and provides a quantitative measure of the 
properties of the feature (mensuration). 

The capability ratings in Table 9 assume near optimum conditions 
because all methods will yield inferior information if used under 
adverse environmental conditions or improperly located with respect 
to the feature. For example, an aerial photograph taken on a 
cloudy day would be inferior to one taken under good visibility 
conditions. A boring sited to intercept a fault might yield valu- 
able information if the fault is crossed and less important infor- 
mation if the fault is missed. The capability rating represents 
the highest quality information that the technique can provide. 

The capability rating of most of the methods is "3" or less 
even under optimum conditions, which indicates that most methods 
have the capability to identify and partially locate, but not to 
measure, the significant geologic features. In general, ground 
surface methods and remote sensing methods have low to intermediate 
ratings, borings have intermediate ratings, and exploratory exca- 
vations and field tests performed primarily in exploratory exca- 
vations have the highest ratings. 

Remote sensing and surface mapping methods are given lower 
ratings because the exposed material is normally altered by surface 
weathering and is under lower stress conditions than the material 
in the subsurface. Almost invariably projection of surface geo- 
logic features to tunnel level involves uncertainty as to location 
and characteristics in the subsurface that cannot be resolved until 
the material is exposed in the tunnel. Surface and airborne geo- 
physical methods are given a low rating because they provide only 
an indirect measure of subsurface conditions (it is important to 
note that these are measurements, even though indirect, rather than 
inferences). Borings are given an intermediate rating because they 

172 



provide essentially a one-dimensional sampling of the subsurface 
materials and are generally limited to some extent by sample losses 
and sample disturbance. Exploratory excavations are given high 
ratings because these man-size openings provide access for observing 
the three-dimensional layout of subsurface features and the behavior 
of the material in a tunnel. Field tests are also highly rated 
because these tests provide a quantitative measure the response of 
a medium to large scale section of the rock mass to compressional 
loads, shear loads, or percolation. 

Table 9 also indicates that the investigation methods with the 
higher capability ratings costs more. Exploratory excavations and 
some field testing methods are the most expensive with progressively 
lower costs for borings, geologic mapping and aerial photograph 
interpretation. Logically, most tunnel site investigations will 
involve the maximum use of the lower unit cost methods and minimum 
use of the higher unit cost methods. 

Using the terminology developed for conventional methods, it 
is evident in Table 9 that the remote sensing methods have a low to 
intermediate unit cost and have low to intermediate capability 
ratings. These observations suggest the following conclusions with 
respect to the application of remote sensing methods to tunnel site 
investigations. 

a. Remote sensing methods have the same general limitations 
as other surface investigation methods. 

b. Remote sensing methods can supply some information more 
completely, cheaply, and quickly than surface methods. 

c. Some remote sensing methods, such as SLAR, have high unit 
costs with respect to other surface methods. 

d. Remote sensing methods do not have a sufficiently high 
capability rating to replace borings or exploratory 
excavations. 

e. Certain remote sensing techniques, when used in con- 
junction with conventional tunnel investigative methods, 
increases the reliability of the three-dimensional model 
of the tunnel site. 



9.5 Cost Effectiveness of Combined Conventional and Remote Sensing 
Systems 

Cost is a major consideration during the planning and execution 
of a tunnel site investigation. While the budget for a tunnel site 

173 



investigation is generally large in contrast to budgets for founda- 
tion investigations or investigations for shallow surface excavations 
such as highway cuts, the funding does sometimes limit the type and 
extent of the site investigation. The budget for the investigation 
work is normally established in the planning stage based upon a 
preliminary assessment of the geologic conditions, the investigation 
goals, and the type and extent of investigative work to be performed. 
As the work progresses, an improved understanding of geologic 
conditions at the site often leads to a revision of the investigation 
plan and some strain on the funds available. 

An investigator using conventional and remote sensing methods 
must give consideration to the following questions in planning and 
performing a tunnel site investigation: 

1. What proportion of available funding should be used for 
remote sensing? 

2. Will remote sensing provide an adequate geologic infor- 
mation base to guide or decrease the conventional in- 
vestigation work? 

3. Will the remote sensing information have a tangible 
influence on the cost of tunnel construction? 

There are no universally valid answers to these questions but the 
following paragraphs may be of some assistance. 

The response to the first of these questions is the amount of 
funding will be dependent upon the potential value of the results. 
It should be recognized that remote sensing methods will generally 
be most useful to the investigation if they are used during the 
early part of the program. The relatively inexpensive, small-scale 
satellite imagery and available black-and-white photography should 
be obtained and analyzed during the planning stage of the project. 
This imagery should be used regardless of the level of detail of 
existing information available for the site. In almost all in- 
stances the imagery will provide a perspective that is not provided 
by existing information. 

In all areas where there is little information from previous 
conventional investigations, the imagery will provide insight into 
the geologic and regional setting and will serve as an initial 
basis of planning for subsequent investigations. In all but a \/ery 
few instances it will be desirable to plan for the acquisition of 
additional remote sensing data prior to surface investigations. 

After the initial regional surface mapping, the investigator 
should evaluate the contribution of the less expensive forms of 
special remote sensing data. If SLAR imagery is available for the 
site (see Appendix H) it should be ordered. If SLAR does not 

174 



exist, acquisition of LSAP imagery should be planned as part of the 
initial program of photographic data acquisition. The initial 
acquisition program should also include either color or color 
infrared imagery at medium and large scales. The value of the 
information contained in these data far outweighs their moderate 
cost in almost all environments. If hydrologic problems are known 
to exist or are suspected, thermal infrared scanner imagery should 
be included in the initial remote sensing data acquisition. If the 
area is known to contain major fracture zones, serpentine bodies or 
basalt dikes, AEM may also be incorporated. 

The response to the second question depends on the site being 
investigated. Assuming that remote sensing techniques are used, 
preliminary interpretation of the initial data set will enable the 
planning and direction of the surface geologic investigation, 
thereby making optimum use of time and resources. This optimization 
is possible because the geologist has become intimately familiar 
with the area during the photo interpretation phase of the investi- 
gation; he has placed the site geology into a regional setting, and 
has identified and located specific hazards or problem areas that 
require special attention. The result is that the entire field 
operation becomes more efficient and productive. The amount of 
field time that is usually spent in trying to locate fracture 
zones, contacts, and thick alluvial or colluvial deposits is greatly 
reduced. 

Following the surface investigation and prior to the beginning 
of the subsurface investigation, field and remote sensing data 
should be integrated to produce a three-dimensional model of sub- 
surface conditions. This integrated interpretation should be used 
to plan and guide the subsurface investigation and to determine the 
need to use the more expensive forms of remote sensing such as AEM, 
EM, MSS, and TIR. At this stage, the investigator will have a 
sufficiently detailed concept of the site conditions to realistically 
appraise the contribution of these additional remote sensing methods. 

Table 10 summarizes the response to the third question. The 
table compares the units of exploratory work and the units of 
construction work which could be purchased for $10,000 in 1975. 
The sum of $10,000 was selected as being a normal increment of cost 
for remote sensing data acquisition and analysis. 

The unit prices shown in Table 10 do not refer to a specific 
site or a specific set of geological conditions, but rather they are 
presented as representative of typical investigation and construction 
costs. The sum of $10,000 will provide one of the following con- 
ventional investigations; a field geologist's time to map most 
tunnel sites; seismic testing along a major portion of a tunnel 
alignment; one or two deep borings; or the excavation of a short 
section of exploratory adit. Ten- thousand dollars of remote sensing 
imagery and interpretation is sufficient to provide an analysis of 

175 



Table 10 Comparison of Investigation and Construction Cost 
(Reference amount is $10,000 at 1975 prices) 



Units 
50 man days 
5,000 linear ft. 
400 linear ft. 
20 linear ft. 
20,000 sq. mi. 
25 sq. mi. 



Investigation 
Unit Cost ($) 
$ 200/day 
2/ft. 
25/ft. 
500/ft. 
0.50/sq. mi. 
400/ sq. mi. 



Description 
Field geologist for mapping 
Refraction seismic testing 
Nx core drilling and sampling 
Exploratory adit 
Satellite imagery and interpretation 



Acquisition and interpretation 
of LANDSAT, Skylab, SLAR (SAC), 
high altitude B&W, low and medium 
altitude color and black-and-white 
photography and LSAP photography.* 



Construction 



900 man hours 
24 crew hours 
10 linear ft. 

8 steel ribs 

12 days 



; 11/hr. 

415/hr. 
1 ,000/ft. 

1,250/ rib 

830/day 



Miner for tunnel excavation 

38 man crew for tunnel excavation 

Excavate and install basic lining for 
a 35 ft. highway tunnel in poor ground 
conditions 

8 inch wide flange steel rib weighing 
67 lbs. per foot with fittings and 
connectors for 35 ft. tunnel 

Operation of fans to provide normal 
ventilation capacity in a 35 ft. tunnel 



TIR over the same site (acquisition and interpretation) would cost 
about $14,000 and AEM about $30,000. 



176 



the regional and local geology based on satellite photography, 
black-and-white, color and low-sun-angle photography flown specifi- 
cally for the site and SLAR imagery if it previously existed. The 
same $10,000 in construction will purchase a few feet of a single 
bore highway tunnel with the initial support system without lining, 
pay the salaries of a tunneling crew for about 24 hours, purchase a 
few steel ribs, or ventilate a tunnel for about two weeks. 

This comparison between conventional and remote sensing in- 
vestigation costs and construction costs has little meaning until 
one compares tunneling costs with the influence of adverse geologic 
conditions. Tunneling experience indicates that previously unknown 
geologic features such as faults or weathered zones that extend a 
few feet to a few tens of feet along a tunnel alignment can result 
in the installation of additional steel ribs and may create tunnel- 
ing delays which range from a few hours to a few days. A previously 
unknown zone of adverse geological conditions ranging in length 
from tens of feet to hundreds of feet can create extra support 
costs and delays which can range from $10,000 to easily over a 
million dollars. While knowledge of adverse geologic features will 
not change the character of the work required, this knowledge can 
prevent the adoption of tunnel designs which are not appropriate 
for the geologic conditions and can prevent construction delays. 
If, therefore, previous investigations indicate the possibility of 
adverse geological conditions, but do not completely document their 
location or characteristics, an additional investment in the site 
investigation of $10,000 to $30,000 could result in construction 
cost savings much greater than the investment in the investigation. 

To summarize, once the engineer is familiar with the capability 
of remote sensing techniques, it will become apparent to him that 
these techniques can be used to provide new information, augment 
the data commonly acquired using conventional site investigation 
techniques, and to guide conventional site investigation programs. 
The synoptic characteristic of airborne data will be helpful in 
directing surface investigations from general surface mapping to 
ground geophysical surveys and rock borings. The information 
obtained by integrating the two techniques will be more valuable 
and effective than the information obtained separately by either 
technique. The incremental cost of site investigation should be 
weighed against the incremental cost of delay that can result from 
insufficient data. The additional increment of investigation cost 
using an integrated investigation approach may save many increments 
of construction costs. 

The final assessment, therefore, is remote sensing techniques 
can be combined with conventional investigation techniques to 
produce the best and most cost effective description of tunneling 
conditions. 



177 



10.0 CONCLUSIONS 

The following are the principal conclusions arising from this in- 
vestigation: 

• Inclusion of remote sensing techniques into the process of 
selecting and geologically evaluating a tunnel site will be 
most effective when thoroughly integrated with conventional 
techniques. 

• Aerial remote sensing techniques can provide a substantial 
amount of information for developing a three-dimensional 
geologic model and aid in tunnel location and design. 

• Analysis of the capability of a variety of airborne and satel- 
lite systems, demonstrates that certain geologic features are 
more readily detectable with one system than another. However, 
because the capabilities often overlap there can be flexibility 
in selecting an array of sensors for gathering the required 
information. Therefore, selection of an optimum remote sensing 
system for site investigations will depend on the specific 
conditions at a site. 

• Computer analysis of geologic data acquired during this study 
indicates that this approach can be extremely useful in certain 
areas. However, we conclude that the full potential of computer 
analysis of geologic data cannot be demonstrated using data 
from the two test sites selected for this study. 



• 



The effectiveness of a remote sensing system is related to the j 
capability of that system and the need for the information i 
supplied by that system. The cost of a system is more prac- 
tically considered in terms of percentage of total project I 
cost, or compared to increments of construction cost. If an i 
additional increment of site investigation cost has the poten- * 
tial of avoiding 10 increments of construction costs, (for ' 
example, slower drive rate, additional roof support), or 
avoiding delays that cost many times more than the investi- 
gation increment, then the additional increment of investi- i 
gation should be spent. 1 



The above conclusions require some qualification. Satellite and 
aerial remote sensing techniques can provide only a partial description 
of the advantages and disadvantages of a certain route and a partial 
description of the tunneling conditions at a specific site. Realistical- 
ly, remote sensing techniques cannot replace conventional investigation 
techniques, but when the two are thoroughly integrated the results are 
more reliable and valuable than those that could be achieved by either 
method separately. 



178 



Another premise that was established early in this study was that 
there is no optimum combination of sensors that can be recommended and 
applied to all proposed tunnel sites. It is possible, however, to make 
a conditional recommendation of sensors to be used at various stages of 
a tunnel site investigation. 

Because the costs of conducting remote sensing surveys and analyzing 
the data vary considerably, the most realistic approach to an economic 
analysis would deal with the costs of investigation relative to the costs 
of construction. The cost-effectiveness conclusions are based on semi- 
quantitative estimates of costs for acquiring and analyzing data from 
several types of remote sensing systems. These remote sensing costs are 
low compared to the cost of constructing the tunnel. A single unit of 
investigation cost may save many units of construction costs that are due 
to unpredicted hazards. 

The remainder of this discussion will be an expansion of the points 
above, and specific conclusions on the utility and contribution of 
various remote sensing techniques when used separately or in combination. 

Satellite data, both LANDSAT and Skylab, are useful for tunnel route 
selection and regional geologic analysis. Regional geologic features 
that are interpreted on satellite data invariably have smaller scaled 
features associated with them, and these smaller features can have direct 
impact on the tunneling conditions at a specific site. Satellite data 
allow gross regional estimates of lithology and hydrology, but satellite 
data are most effective when used in conjunction with larger scale aerial 
photography and imagery. Because the cost of satellite data is low, the 
information is extremely cost-effective and should invariably be acquired 
for route and site investigations. 

The all weather capability of side-looking airborne radar (SLAR) is 
valuable in areas where there is a high percentage of cloud cover through- 
out the year. With the higher resolution and synoptic view of the terrain 
provided by SLAR imagery it is possible to make regional geologic analyses 
of greater detail than those attainable from satellite imagery. SLAR 
data is particularly useful for identifying topographic expressions of 
structural features. As with satellite data, however, SLAR imagery is 
more effective when it is used with larger scale photography and imagery. 
Acquisition of new SLAR data is normally too expensive for a specific 
site unless the area is cloud covered to the extent that other imagery 
cannot be obtained. Therefore SLAR, although it can be very useful for 
tunnel route and site selection, is recommended only if it is already 
available. Only then will it be cost effective. 

The appearance of low- sun-angle photography (LSAP) is similar to 
that of SLAR imagery. The spatial resolution of LSAP is higher than SLAR 
imagery as it is normally acquired at a larger scale. It thus provides 
shadow enhancement to small structures of interest to tunnel site in- 
vestigations. LSAP is most useful when it is used in combination with 

179 



other photographic data. It is relatively inexpensive to acquire and can 
be effectively substituted for SLAR data. 

Black-and-white panchromatic photography obtained with a metric 
camera provides the best spatial resolution and geometric fidelity of all 
the sensors employed in this study. This photography is useful for 
stereoscopic plotting of topographic maps and for transfer of photointer- 
preted geologic and hydrologic information to the topographic base maps. 
Spatial resolution of large scale, black-and-white, panchromatic photo- 
graphy permits the detailed mapping of the stratigraphy and structure 
when it is visible at the surface. The cost of acquisition and proces- 
sing of such photography is the most economical of all of the photography 
and imagery acquired during this study. 

Color aerial photography is an essential data type for site investi- 
gations. Its prime utility is in the identification of lithologies, 
structural features, soil types, and vegetation. When used in combination 
with other systems such as LSAP and black-and-white panchromatic photo- 
graphy the structural and stratigraphic map produced will be as compre- 
hensive and complete as is practical to be obtained with the more standard 
remote sensing methods. This information will contribute to an under- 
standing of the relationships between subtle tone differences in rock 
types or soil types. The cost of color film and processing is greater 
than that for black-and-white, but the added expense is more than offset 
by the gain in information. 

Color infrared photography is the most useful type of photography 
for the identification of vegetation type, vigor, and phenological stage 
of development. Vegetation patterns are largely controlled by the type 
of soil and availability of soil moisture and these patterns may mark 
fracture zones in some instances. The presence of certain vegetative 
types may indirectly indicate the chemical composition of the soil. The 
concentration and type of vegetation can provide information about the 
surface hydrology, soil moisture patterns, and possibly the landslide 
potential of the slopes in the area of planned tunnel portals. Due to 
the limited color range of rock and soil as rendered on the false color 
image of color infrared photography, some misinterpretation of these 
features may occur if the analysis is based on this type of imagery 
alone. The cost of acquisition and processing of color infrared photo- 
graphy is similar to that for color aerial photography. 

Although acquisition of multiband photography was not originally 
part of this investigation, it seemed desirable to acquire multiband 
photography as a demonstration of an alternative to multi spectral scan- 
ning systems. Consequently, we acquired limited multiband ground photo- 
graphy. This photography demonstrates that multiband photography can 
produce a color composite image that is wery nearly the true color of the 
scene, yet maintain a high spatial resolution similar to that of black- 
and-white panchromatic photography. The flexibility in producing the 
near true color format and the additional capability of generating color 
infrared and a variety of composites suggests that it is possible to 

180 



satisfactorily substitute multiband photography for black-and-white 
panchromatic photography, color aerial photography, and color infrared 
aerial photography with actual improvement of interpretabil ity if com- 
parable scaled imagery is obtained. The cost of acquiring and processing 
multiband photography is higher than it is for the acquisition and pro- 
cessing of color aerial photography. Limited availability of camera 
systems accounts for most of the cost increase. The analysis must also 
be performed with specialized color additive viewers and production of 
hardcopy requires the services of a specialized photolab. If these 
facilities are available, the use of multiband photography in lieu of 
black-and-white panchromatic, color, and color infrared can perhaps be 
the most cost effective approach to airborne remote sensing. 

Multispectral scanner imagery is most useful in areas where rock 
outcrops exist and where those outcrops are not obscured by vegetation, 
lichen, desert varnish or other surface contamination. Lithologic analy- 
sis and rock type discrimination are largely restricted to outcrops that 
are relatively fresh, but this phenomenom is uncommon in the field. The 
utility of multispectral scanning imagery is increased by the fact that 
the images are recorded on magnetic tapes, which permits computer enhance- 
ment of the images. However, the resolution remains relatively low. 
Enhancement of the imagery may include ratioing between spectral bands to 
highlight differences in the spectral signatures of various targets. 
Because multispectral scanner data is relatively expensive to acquire and 
analyze, its use in tunnel site investigations, in most situations, 
cannot be justified. 

Thermal infrared scanning systems which operate in the 8-14 m 
spectral range sense emitted rather than reflected infrared radiation. 
This capability can be used effectively in tunnel site investigations for 
the identification of soil moisture differences which are characteristic 
of fracture zones in the rock and which may be detectable through a thin 
soil cover. The identification of areas of high soil moisture may also 
indicate zones of potential slides and slump. As used in this investi- 
gation, thermal imagery provided unique information concerning the 
chemical composition of rocks within the area of interest. The practical 
value of this capability is limited in most tunnel site investigations 
because a visit to the site, which must be made, will answer questions of 
rock composition. 

Data from a thermal scanner system, like the multispectral scanning 
system, is relatively expensive to acquire and process. Generally, 
thermal infrared scanning data would not be acquired unless, based on 
preliminary geologic analysis of the site, hydrologic problems are antic- 
ipated. 

Airborne geophysical systems (electromagnetic and magnetic) were the 
only systems used in this investigation that provided direct information 
about the subsurface. These systems are particularly good for detecting 
certain classes of features such as wet fault or fracture zones, con- 
ductive strata such as graphite bearing rocks, or other lithologies 

181 



possessing magnetic properties that indicate zones which may pose major ' 
construction problems and increased costs. Electromagnetic systems 
detect differences in resistivity in near-surface rock and in soils, and 
are, therefore, potentially valuable tools for tunnel site investigations. 
AirtDorne magnetometers systems record remnant magnetization and differences 
in the magnetic susceptibility of subsurface soil and rocks. This is an j 
important capability for tunneling applications in that it makes it 
possible in some situations to infer the displacement of lithologic units 
across faults. It also allows some discrimination of rock types and j 
recognition of major discontinuities. Both airborne geophysical systems '', 
should be flown together. The cost addition of aeromagnetics when added ' 
to the airborne EM system is negligible. Airborne geophysical data will 
be most effective when used in conjunction with data from other airborne 
sensor systems. 



182 



11.0 RECOmENDATIQNS 

11.1 Recommended Sensor Compliment 

Selection of sensor types is largely dependent on the geological, 
hydrological , and climatological conditions at a specific site. The 
utility of a sensor may vary as the environmental conditions vary. 
It is, therefore, difficult to recommend an optimum compliment of 
sensors for all sites; however, some conditional recommendations of 
sensors can be made. These recoirmendations are based on the cost of 
aquisition, cost of processing and interpretation, and the effective- 
ness of the sensors. There are three reconmended categories of 
remote sensing data: 

Category 1. Data from these systems should be acquired for all 

sites if continuous cloud cover, haze or fog does not 
occur. 

Category 2. These systems should be used only if severe 

hydrologic problems are anticipated or if the surface 
geologic structure is sufficiently complex that only 
subsurface data will make the three-dimensional 
geologic model more reliable. 

Category 3. This system should be flown at a specific site only 

if clouds, fog, or haze prevent or hamper the acquisi- 
tion of data by other sensors, and if conventional 
ground techniques are deemed inadequate. 

Category 1 remote sensing systems include; 

LANDSAT Color Infrared Photography 

Sky lab LSAP 

Black-and-white Panchromatic 
Photography Multiband Photography 

Color Photography Existing SLAR 

All of these systems are photographic except LANDSAT multi spectral 
scanner imagery and SLAR data. LANDSAT imagery and Skylab photo- 
graphy should be obtained because of the low cost and the valuable 
route selection and regional geologic information that these systems 
provide. Metric black-and-white panchromatic photography should be 
obtained for stereoscopic plotting, and for its high spatial resolu- 
tion and geometric image fidelity. Color should be acquired for 
best lithologic and soil discrimination. Color infrared photography 
can provide valuable data on vegetative vigor and geologic structure; 
the selection of the appropriate season for acquisition of data is 
more critical than for other photography. Multi band photography 

183 



should be obtained instead of black-and-white panchromatic, color, 
CIR, if the facilities for interpretation are available. Many of 
the capabilities of these airborne photographic systems can be 
duplicated by multiband photography with proper color additive 
viewing and photolab processing techniques. 

Low sun angle photography probably should be acquired at all 
sites. The solar azimuth, which is dependent on the time of the 
year, is important for proper enhancement of structural and topo- 
graphic features. The time of acquisition will vary from site to 
site. 

Existing SLAR imagery from government sources is inexpensive 
and should be acquired if available. LSAP and SLAR systems provide 
similar information; although, SLAR has poorer spatial resolution, 
it provides a shadow-enhanced, synoptic view of the regional geo- 
logic structure and topography. 

Category 2 remote sensing systems include: 

Two channel thermal infrared scanner (8-10ym/10-12ym) 

Multi spectral scanner 

Airborne geophysical (electromagnetic, magnetic) 

Two-channel thermal infrared scanning data is an order of magnitude 
more expensive to acquire, process and interpret than color photo- 
graphy, but if hydrologic problems are suspected or anticipated, 
the detection of potentially "wet" fractures and anomalously high 
concentrations of soil moisture may help to avoid delays during 
construction. Multi spectral scanning surveys are comparable in 
cost to thermal surveys, but much more data is normally acquired, 
consequently, the processing and analysis of the data can be sub- 
stantially more expensive. Although interesting geological infor- 
mation can be derived from these data, e.g., the accentuation of 
the iron-oxide concentrations in certain strata at the Carl in 
Canyon site, the utility of this information to tunnel siting 
studies is negligable. Other features of surface geology are more 
readily and accurately mapped on high resolution aerial photo- 
graphy. This system is not recommended for tunnel site investi- 
gations because it does not contribute cost effective data or 
improve the three-dimensional geologic model. 

Airborne geophysical (AEM) surveys should be conducted in 
geologically complex areas, e.g., if it appears that groundwater 
flow may be a problem or if graphitic or other conductive zones are 
present that could represent areas of structural weakness. Airborne 
magnetometer data should be acquired in conjunction with AEM surveys 
to support and improve the three-dimensional geologic interpretation. 
Airborne geophysical systems are expensive, ranging from 10 to 20 

184 



times more than a color photographic survey, but they may contribute 
to a cost savings by optimizing the surface geophysical and rock 
boring program analysis. 

The third category sensor is side-looking airborne radar. 
Since much of the equipment is bulky and normally requires sophisti- 
cated aircraft, the acquisition of SLAR is wery expensive. Survey 
costs range from 15 to 30 times more than for color photography, but 
if imagery does not exist for a given site, it should be acquired 
only if cloud conditions make acquisition of other airborne data 
impractical. Perhaps the only other unique capability that might 
make acquisition of SLAR worthwhile is that the variation in look 
angle for SLAR is not dependent on solar azimuth as is LSAP. 

Actual application and experience in the use of remote sensing 
systems to tunneling investigations will improve future recommen- 
dations of sensor complements. The final evaluation of the cost 
effectiveness of the systems will occur only after tunnel construc- 
tion. If geological conditions are simple and few delays and hazards 
occur, then the Category 1 remote sensing systems are most cost 
effective and should be used. If geological and hydrological 
conditions are complex. Category 2 systems will reduce the probability 
of encountering unexpected hazards and delays and they become cost 
effective. The use of Category 3 systems is based almost entirely 
on climatological conditions at the site. If satellite or airborne 
data cannot be collected then the expensive SLAR systems may become 
cost effective. 



11.2 Considerations of Seasonal and Diurnal Effects 



Seasonal and diurnal effects related to climate vary with 
geographic location. This statement is of course obvious, but it is 
the basis of the observation that a single recommendation of optimum 
time of year or day to acquire remote sensing data is meaningless 
unless it is related to a specific site. The conditions that vary 
with the season and time of day can affect visibility, alter emitted, 
reflected and transmitted energy, and affect the stability of the 
aircraft carrying the sensor. 

Rather than attempting to consider all possible combinations of 
seasonal and diurnal variables in making a recommendation, the 
variables themselves and their influence on the sensors will be 
presented. With this information, and climatological and meteoro- 
logical data for a specific site the geologist or tunnel engineer 
will be able to select the proper time to acquire remote sensor 
data. 



185 



The seasonal and diurnal conditions to be considered when 
planning a remote sensing mission include: 

Surface moisture * Clouds 

Snow cover * Haze/fog 

Surface temperature * Phenol ogical stage 

Air temperature of vegetation 

Wind • Solar elevation 

Sferics and azimuth 

Humidity 

Surface moisture differences will change the tonal character of 
most targets in the visible and near-visible range of the spectrum. 
Therefore, imaging and photographic systems that operate in that 
range may produce different images of the same target under different 
surface moisture conditions. In most instances there is no distinct 
advantage to imaging an overall wet or dry surface, but it is im- 
portant to be consistent when obtaining data from different sensors 
at different times. Surface moisture increases the radar reflec- 
tivity of the target thereby masking detail of the image. It is 
recommended, therefore, that when possible, radar imagery should be 
acquired during a period when surface moisture is low. Surface 
moisture affects the information that can be obtained using thermal 
infrared scanners by either highlighting or supressing structural 
geologic features. Such scanners are most effective when minor or 
moderate amounts of soil moisture are present. If soil moisture is 
excessive the thermal gradient between emitting surfaces will be 
considerably reduced, minimizing the contrast between target materials, 
Surface moisture also affects airborne geophysical surveys, speci- 
fically, resistivity surveys. It can increase the conductivity of 
the surface materials, giving spurious surface information as well 
as obscuring the detail of subsurface information. If there is in- 
sufficient or excessive surface moisture, fractures and sinkholes 
may go undetected. 

Snow cover has the effect of either increasing the interpreta- 
bility of imaging and photographic system data or it can obscure 
important geologic information. A certain amount of snow cover, 
e.g., less than two inches, will enhance topographic and geologic 
features on satellite imagery, aerial photography, and mul tispectral 
scanner data. If the snow is too deep it will obscure significant 
geological features on imagery from these types of sensors. With 
radar imagery some penetration of the snow cover can be expected. 
However, if the snow is extremely wet there may be some increased 
reflection from wet surfaces. Snow cover affects airborne geo- 
physics in that wet snow may increase the conductivity of the 
surface and near-surface materials. Snow enhancement of geologic 
features is difficult to plan for because the amount of snow cover 
for proper enhancement can rarely be predicted in time to organize 
a photographic mission. 

186 



Surface temperature has little effect on radar, satellite 
imagery, aerial photography, or airborne geophysical data; however, 
it does affect the information obtained by thermal infrared scanning. 
Surface temperatures are generally a direct result of solar heating. 
Differential insolation effects on the ground surface due to topo- 
graphic shadowing can generate a thermal image similar to that 
acquired by low-sun-angle aerial photography. This is, in effect, a 
thermal shadow enhancement of geologic and topographic features. 
Differential cooling of the surface, notably in fracture zones which 
generally appear cooler due to moisture concentrations, produce 
surface temperature anomalies important in geological mapping. 

Actual air temperature has little effect on the sensors used 
during this investigation except for the thermal scanners. There- 
fore, it is a relatively insignificant consideration in planning 
most remote sensing missions. The air, although transparent and 
undetectable in the 3-14ym spectral range, can transfer heat to or 
from a target material and influence the detected temperature. This 
is particularly so if there is an appreciable difference between the 
air and ground temperatures or if there is substantial air movement. 
A knowledge of those conditions that prevailed at time of data 
collection is essential to effective data analysis. 

Wind has no effect on orbital platforms, but does have con- 
siderable effect on radar, photographic, scanner, and airborne 
geophysical systems. Obtaining good quality information (geometric 
image fidelity and proper orientation of imagery) is dependent upon 
a stable platform; therefore, surveys should not be conducted 
during excessively high winds. In some geographic locations, 
certain times of the year are characterized by high winds, those 
periods should be avoided when possible. 

Sf erics are the natural fluctuations of the electromagnetic 
field of the earth; they are caused by lightning discharges on a 
global scale. Sferics affect only the airborne electromagnetic 
system that was used during this investigation. For this reason the 
airborne geophysical surveys should not be conducted during times 
when excessive electrical activity exists. An auxilliary sferics 
monitor should be used. 

Humidity affects thermal scanning systems; however, the humid- 
ity has to be extremely high (85-100%) before' thermal radiation in 
the 8-14um range is attenuated significantly. 

Clouds obscure the ground from orbital and airborne platforms. 
They do not, however, affect radar imagery unless condensed water 
vapor is present in the clouds in appreciable quantities. Clouds do 
not directly affect airborne geophysical sensing, but such surveys 
are conducted at low altitudes where good visibility is essential. 
Partial cloud cover can be tolerated on some photographic missions, 
but the illumination of the target area may be affected and, con- 
sequently, the color balance. Cloud shadows within the target area 

187 



can degrade daytime thermal infrared imagery and may result in 
misinterpretation. This statement applies to LSAP also, particu- 
larly if thin cirrus clouds cast linear shadows which could be 
interpreted as ground features. 

Haze and fog can severely attenuate reflected and emitted 
energy. Satellite and airborne photographic and scanner data will 
have less resolution and clarity and detail if acquired during haze 
and fog conditions. Haze and fog, however, do not affect airborne 
geophysical or radar systems. 

Stages of phenological development of the vegetation are im- 
portant to all systems used during this investigation except airborne 
geophysics. Vegetation can either obscure or enhance structural and 
topographic detail. For geological analysis (lithology, structure, 
stratigraphy) it is recommended that in areas where leaf canopy can 
be a problem the aerial photography be acquired during the late 
winter or early spring. This is the period of maximum leaf com- 
paction on the ground and before spring leaf development. For 
hydrologic investigations, color infrared imagery should be obtained 
in the spring as the leaf canopy begins to develop. In arid regions 
vegetation may reflect subtle changes in soil composition and mois- 
ture content. This, in turn may emphasize lithologic differences 
and structural features. Consequently, the best time to acquire 
this type of photography in areas of low precipitation is during the 
wetter season. Geobotanical indicators are often used to identify 
varying amounts of soil moisture and chemical properties of the 
soil. These above factors apply to satellite and airborne photo- 
graphic and scanner data. On radar imagery vegetation has the 
effect of altering the texture of the image. Geophysical systems 
are not affected by vegetation. 

For passive imagery systems solar elevation and solar azimuth 
have the effect of enhancing topographic and geologic features 
provided that the solar elevation is low enough (10° to 25°) to cast 
a substantial shadow. Radar and geophysical systems, however, do 
not depend on solar energy for operation. 

The influence of seasonal and diurnal conditions on the quality 
of remote sensor data will vary with the severity of the condition 
and the system used. In many instances these conditions can be 
tolerated if they are unavoidable, but it is necessary to be aware 
of the influence that the particular condition will have on the 
quality of the data. Based on this brief sunmary of seasonal, 
diurnal, and climatic effects on various remote- sensing systems and 
the reconmended procedures for acquiring data, the engineer or 
geologist can select sensor types for almost any proposed tunnel 
site. 



188 



n.3 Recommendations For Future Work 

In a report such as this it is difficult to be totally com- 
prehensive in evaluating all of the capabilities of commercially 
available airborne remote sensing systems. Furthermore, it is even 
more difficult within the scope of this report to describe the 
details of selecting sensors under all environmental conditions, 
contracting for services, interpretation of data, and application of 
results to tunnel site investigations. Therefore, we believe that 
the work begun during this contract should be continued and expanded. 
Our recommendations for future work are:. 

• Selected remote sensing techniques should be applied to 
additional tunnel sites to verify their utility in dif- 
ferent geologic environments; 

• A remote sensing handbook for tunneling should be prepared 
for agencies who may be preparing bids and contracts and 
contracting for the construction of tunnels and for orga- 
nizations involved in the construction of tunnels. 

The additional site should be in a more complex nonsedimentary 
geologic environment. The handbook would describe in laymen's terms 
how various remote sensing techniques can be applied during the 
feasibility and final design investigations for tunnels, and include 
information on relative cost and utility of the sensors examined, 
given a variety of geologic environments. 

Remote sensing techniques were applied in this study to two 
tunnel sites, one in the Eastern and one in the Western United 
States. These sites were selected for a variety of reasons including 
the fact that remote sensing data could be collected for each site 
during optimal seasons and within the performance period on the 
contract. Unfortunately, both sites are in relatively similar 
geologic environments and both involve relatively simple geologic 
structure. The fact that positive results on the application of 
remote sensing in these two instances were obtained, lead us to 
believe that these techniques should be tested in other more complex 
geological environments. By the addition of such sites the relia- 
bility and utility of the sensors tested could be further substan- 
tiated and extended. The present sites were not adequate to fully 
test the capabilities of some of the sensors examined (notably 
airborne electromagnetic and thermal infrared) and their potential 
contributions to tunneling. Airborne multiband photography was not 
used at either site because of its expected duplication of multi- 
spectral scanner data. Based on our use of ground multiband photo- 
graphy at Carl in Canyon, we believe that airborne multiband photo- 
graphy may provide an inexpensive but effective substitute for 
multispectral imagery. Additional sites would provide the opportu- 
nity to compare the two sensor systems. 



189 



The additional sites should include at least one in a crystal- 
line terrain - that is, in igneous, metamorphic or volcanic rock. 
Such sites should adequately test and demonstrate capabilities of 
the recommended sensors beyond those capabilities demonstrated in 
sedimentary rock. The sites can be an existing or proposed tunnel 
but it need not be a highway tunnel. It could be for water or rail. 
Several candidate sites include: 

• The Straight Creek tunnel, which was among those considered 
originally, 

• The Caldecott highway tunnel, in California 

• The Berkeley Hills BART tunnel, California area, 

• A water tunnel in California 

Potential users of the results of this investigation will 
require some assistance in applying the results to specific siting 
and engineering problems. Although this final report documents the 
capabilities of the various sensors tested as well as recommends 
situations in which those sensors may be most usefully employed, we 
believe that a shorter and more general handbook (one that could be 
used by tunneling engineers and understood by managers with a variety 
of technical backgrounds) is required if these techniques are to be 
applied in operational programs. Such a handbook would contain 
easily understood text, tables and charts which would assist the 
user in planning remote sensing missions designed to increase know- 
ledge of a particular site or sites. 

It is clear from these investigations that there is no single 
optimum combination on airborne sensors which might be applied to 
any potential tunnel site. The sensor complement and capabilities 
of selected sensors will vary from area to area depending primarily 
on the geology, climatic environment and vegetation cover of the 
area. Geologists and engineers having less than a full understanding 
of the techniques employed will, with the handbook, be able to 
select a combination of sensors and design a remote sensing program 
which will provide the information they require for engineering and 
construction purposes. 

The information in the handbook should be presented in such a 
way that engineers involved in site selection might derive the 
maximum benefit from remote sensing. This would require a descrip- 
tion of the capabilities and limitations of each of the sensors as 
well as a discussion of their relative cost and a listing of firms 
which provide those services. In addition, some discussion of the 
variety of geologic conditions likely to be encountered in tunnel 
site selection and engineering and the utility of each of the 



190 



sensors for those given conditions should also be included. Specific 
examples of each sensor and the information extracted as well as a 
discussion of problems associated with data acquisition for each 
sensor should be included. Specifically, data acquisition constraints 
such as time of day, season, and weather conditions would be indicated. 

Because purchasing services from remote sensing companies will 
be an uncommon experience for most firms involved in tunnel construc- 
tion, some advice regarding the technical aspects and contract 
specifications should be provided. This discussion should provide 
general guidance to the engineering or tunneling firm on mission 
planning, contractor selection, flightline layout, incorporation of 
corollary data and ground support. While it is recognized that in 
most instances the actual analysis of the data may have to be done 
by specialists familiar with tunnel engineering problems, geology, 
and remote sensing, it is necessary for those contracting for remote 
sensing services and employing remotely sensed data in solving 
engineering problems to understand the techniques employed and the 
conclusions drawn. It is also necessary for the user to specify 
that the data and analysis requirements be met with a report, models 
or maps which satisfy his specific needs. 

To summarize, an outline of the remote sensing handbook for 
tunneling should include the following: 

Application of Techniques 

Capabilities, Limitations, Problems in Acquisition 

Geologic Environments 

Selection of Sensors 

Examples of Sensor Data 

Presentation of Remote Sensing Analysis Data 

Mission Planning - Flight Lines, Contractor Selection 

List of Flying Companies and their services (abridged) 

Relative Costs 

Relative Utility (Effectiveness) 



191 



12.0 FIELD VERIFICATION PLAN 

It is clear from the results presented in Section 7 of this report 
that many of the features and anomalies identified in the remotely sensed 
data require further investigation in the field. This section presents a 
plan for verifying the interpretation and inferences made from remote 
sensing data. The goal of this plan is not simply to verify features 
interpreted from the surface, but to extrapolate them into the subsurface 
as accurately as possible. The features to be extrapolated are primarily 
structural and geohydrologic, and include faults, joints, linears, linea- 
ments, sinkholes, and karst topography. Other conditions to be considered 
in designing the field verification plan are seepage through permeable 
rocks or along faults. The most accurate way to verify these features is 
with the aid of an integrated program of surface geologic investigation, 
geophysical surveying and drilling. 

Once a model of the subsurface geology has been postulated on the 
basis of remote sensing data and geological observation, the results of 
the geophysical surveys can then be used to refine the model and optimize 
the selection of the location of core borings and drill holes. It is 
important that they be placed where they have the best chance of inter- 
secting possible problem areas which the subsurface model suggests may 
exist. It is equally important that the holes be logged geophysical ly, 
as well as geologically, in order to obtain the greatest return per foot 
of hole drilled. The following field verification plan is designed pre- 
suming that the tunnels at each test site have not yet been constructed . 
We assumed that this work is being done while the tunnels are being 
designed and that the geophysical and drilling programs are yet to begin. 



12.1 Carl in Canyon Site 

12.1.1 Geology 

The geology of the site has been fully described earlier 
in Section 5.1. The remote sensing data aquired over it has 
been analyzed in Section 7.0. They will be briefly summarized 
here. The two geologic formations present at the tunnel site 
are the Diamond Peak (Upper Mississippian in age) on the 
western end of the tunnel striking N15°W and dipping 85°W; and 
the Strathearn formation (Upper Pennsyl vanian) cropping out on 
the east end of the tunnel, striking approximately N25°W and 
dipping 70°NE. An angular unconformity exists between the two 
formations. The Diamond Peak formation consists predominantly 
of conglomerates and quartzites, which range in thickness from 
three to five feet and are well cemented by chert, quartz, and 
iron oxide. They contain a widely-spaced pattern of joints. 
The thinner interbeds of shale and siltstone are also well 
cemented, and are more closely jointed than the sandstone and 
conglomerate. 

192 



The Strathearn formation is a hard, medium-to-thick- 
bedded limestone with thin inner beds of shale. It is exposed 
on top of the meander spur, on the eastern side of the spur and 
on the eastern canyon wall. Most outcrops of limestone display 
several sets of closley-spaced joints. These joints, bedding 
planes, and shale inner beds all combine to limit the average 
size of the limestone blocks to less than one foot (.3m) in 
most exposures. The rock and natural exposures, however, 
appear relatively stable because the small blocks have an 
irregular shape and high degree of interlock. 

Unconsolidated deposits of sand, gravel, and boulders 
are found at the west portal. These deposits include remnants 
of terraces deposited by the Humbolt River and colluvium which 
has accumulated at the base of the spur. 

More than 11 faults, linears, and lineaments have been 
identified on the imagery. Neither of the two major faults 
identified intersect the tunnel alignment selected. A major 
northwest trending reverse fault crosses the northeastern 
portion of the spur. The fault trace is identified within 100 
ft. (30m) of the proposed eastern portal. The total vertical 
displacement of this fault is approximately 300 ft. (90m). A 
second major fault zone has been identified south of the 
western portal. Neither the displacement along this fault nor 
its dip have been determined from surface mapping, but it is 
not likely to intercept the tunnel. 

Faulting, both cross and parallel to the bedding planes, 
was observed in both formations. The dips of the fault planes 
are unknown, but these noted near the east portal were nearly 
vertical. The displacement along these faulting appears minor 
but the number of faults may be extensive given the proximity 
of the major fault. Such faults do not form to the exclusion 
of others, but instead, as the product of the opening of myriad 
microscopic cracks throughout the rock which are so ordered 
that they propagate in various amounts, some enough to finally 
coalesce to form a through-going fault zone in the midst of 
less through-going fractures (Johnson, 1970). 



12.1.2 Features to be Verified 

The faults mapped from the remote sensing data and 
observed in the field pose the most obvious problem for tunnel- 
ing. The minor faults associated with the major reverse fault 
north of the east portal could lead to blockcaving during 
excavation if there has not been some degree of recementing 
since their formation. Groundwater circulating down the major 



193 



or minor faults or along the unconformity could cause caving or 
flooding during tunneling. However, because of the arid climate 
in this region and the general structure of the ridge as a 
whole, there is probably little chance of encountering ground- 
water at the depths of the tunnel . 



12.1.3 Verification Plan 

Table 11 is a list of geophysical methods, their appli- 
cability to the problems associated with tunneling, and their 
relative costs. The technique that shows the greatest promise 
for detecting groundwater at this site is EM, and for detecting 
dry fault zones and changes in gross bulk modulae, seismic 
reflection. 

The most likely configuration for an EM survey for this 
application would be an active AFMAG system that has a vertical 
transmitting loop with producing frequencies of 130 Hz and 475 
Hz. The portable receiver is tuned to a narrow dynamic range 
centered on each frequency and will show magnetic field strength 
as a vector function of azimuth and dip. Parallel traverses of 
the receiver at right angles to the proposed tunnel direction 
could be run with the transmitting source set up at a location 
near the east portal. The strongest conductors are assumed to 
be water filled fractures, since massive sulfides and other 
conductive rock types are not present in either formation. 

If a serious groundwater problem is suggested by the EM 
survey, it will most likely be localized in a fault zone at 
this site. The fault zone carrying it can best be further 
resolved by a seismic reflection survey. Delineating the fault 
at tunnel depth would require a high-energy, truck-mounted 
source. Portable seismic equipment cannot provide readings 
beyond approximately 200 ft. (see Table 11). The maximum 
thickness of the rock above the tunnel is approximately 500 ft. 
The reflection method is better than the refraction method, 
because of the steeply dipping beds at the Carl in site, and is 
recommended. Possible problems with the reflection surveys are 
that access roads are necessary for operational positioning of 
the seismic trucks, and could be nearly as expensive as the 
survey itself. Offsetting these costs are the value of addition- 
al data obtained by the survey which bear on the bulk material 
properties of the rock. The data will help resolve the frac- 
ture density in the rock along and near the route of the tunnel. 
Additionally, it would resolve the question of the subsurface 
location and dip of the major faults and the angular uncon- 
formity. 



194 



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196 



If the results of the EM survey do not produce any large 
anomalous conductors, the tunneling would most likely not be 
troubled with problems associated with groundwater seepage, and 
there would be no further need to pursue that question. Only 
the question of dry faults and closely jointed shale, siltstone 
and limestone would remain. These questions could best be 
addressed by running a seismic reflection survey using portable 
seismic equipment from above and south of the east portal to 
the reverse fault 100 feet (30m) to the north. This would 
economically provide information on the bulk modulus of the 
Strathearn formation from the surface into the subsurface and 
from the tunnel to the reverse fault, and would indicate any 
change in the density of jointing. This, when interpreted in 
the context of data from three holes drilled to slightly below 
tunnel level, one on the center line of the tunnel and cored 
and two between there and the fault, one beginning in shale and 
one beginning in limestone, each of which should be logged with 
a borehole acoustic log as well as spontaneous potential and 
resistivity, would provide adequate resolution of the question 
of the mechanical properties of the Strathearn. 

Another problem apparent from the remote sensing and 
surface investigations is the Humbolt River terrace materials 
at the west portal. Because of the steep topography of each 
portal and the shallow depth to the target, seismic refraction 
should be used to determine the depth to the soil -bedrock 
interface, and that several shallow boreholes be drilled to 
below tunnel depth and logged with the above mentioned suite 
of logs. This information would be useful in ascertaining if 
rock collapse will occur during and after portal construction. 
It would also be useful in determining the horizontal distances 
over which the tunnel will need support before competent rock 
is encountered. 



12.2 East River Mountain Site 

12.2.1 Geology 

Geology of the East River Mountain tunnel area has been 
discussed in detail in Section 5.2 of this report, and will be 
mentioned only briefly in this section. East River Mountain is 
a ridge capped by Tuscarora sandstone and underlain and over- 
lain by sandstones, shales, and limestones, which strike N65°E 
and dip approximately N25-40° SE. The topography of the lower 
part of the slope is controlled by the overlying and less 
competent Rose Hill shale, the resistant Keefer and Rocky Gap 
sandstones. The upper part of the north slope is a cliff which 
exposes the Tuscarora sandstones. Less steep slopes below it 
are formed by the underlying Juniata shale, Martinsburg shaly 

197 



limestone, and Eggleston, Moccasin, and Gratton limestones. 
The limestones that form a hummocky topography at the base of 
the slope and across the floor of the adjoining valley, and 
have a landscape with limited surface drainage and numerous 
sinkholes, including a line of sinkholes parallel to the 
Cumberland Road and a few hundred feet north of the north 
portal. All of these features indicate the presence of ex- 
tensive solution and groundwater flow between the surface and 
subsurface. The Juniata, Martinsburg, and Moccasin formations 
do not crop out on the northern slope in the immediate area of 
the tunnel because they are covered by residual soils and 
colluvium. 



12.2.2 Features to be Verified 

There are two general problems to be clarified: 1) 
distribution of groundwater in the rocks of the tunnel area, 
and 2) ground conditions in the area, especially in the vicin- 
ity of interpreted fractures. 

The engineering properties of sandstones and limestones 
are generally good except for those containing interbeds of 
shale. The Juniata and Martinsburg shale, which also contain 
shaly limestone and siltstones, although softer than the 
Tuscarora and Keefer sandstones, are relatively competent for 
tunnel excavation and support. However, the shales and silt- 
stones of the Rose Hill formations and the poorly indurated 
sandstones of the Rocky Gap formations are far less competent. 
The limestones are hard and relatively competent except for the 
vicinity of solution openings. 

Artesian groundwater conditions may exist near the south 
portal. Groundwater can be an important element in the overall 
cost of tunneling and its occurrence should be carefully 
noted. Extensive jointing, shear zones, and faulting, coupled 
with formations that are good aquifers, can create difficult 
tunneling conditions, especially if they are not well mapped in 
advance of the actual tunnel excavation. 

The St. Clair thrust fault is exposed approximately 
2,000 ft. north of the north portal. Although this fault zone 
dips SE and so does not cut the tunnel area itself, the lime- 
stones, sandstones, shales, and siltstones at tunnel level are 
undoubtedly fractured and displaced somewhat by related faults. 
These fractures are seen as joints in the outcrops of Tuscarora 
where they are spaced about 10 feet apart. This is fairly 
dense joining for a thick-bedded quartzite such as the Tuscarora 
and indicates that even denser jointing can be expected in the 



198 



less competent and thinner- bedded rock types. If the relation- 
ship established by Harris et al . (1960) holds here, the joint 
density in limestone and sandstone may be expected to range 
from 4 to 8 feet, with the primary effect probably being an 
increase in permeability both laterally and vertically through- 
out the section. It also creates blocks of a size which may be 
a hazard during tunneling if not expected. 



12.2.3 Verification Plan 

Groundwater poses the most important question at the 
East River Mountain tunnel site. A ground electrical resis- 
tivity survey along the proposed tunnel route would help in 
delineating areas of groundwater accumulation and indicate 
locations where boreholes would be most valuable. A dipole- 
dipole survey is least effected by steep topography and would 
be suitable here. It uses a time-domain transmitter and re- 
ceivers coupled with a large power generator (approximately 
40Kw) , and would give the best results. For this amount of 
power an excellent signal-to-noise ratio can be maintained and 
deeper exploration depths obtained than are possible with the 
typical mining resistivity and induced polarization equipment. 
Boreholes located to further resolve the problems of ground- 
water distribution along the tunnel route as delineated by the 
resistivity survey should be logged with spontaneous potential 
and resistivity borehole logs. The data from these sources, 
when integrated with the remote sensing data, would produce the 
best possible estimates for drypack, grouting, padding, and 
other necessary design features. This would greatly aid in 
anticipating other groundwater problems which may be encoun- 
tered during tunneling. 

If severe groundwater and associated caving problems are 
determined to exist by the above model as refined by the 
resistivity survey and accompanying boreholes and geophysical 
logs, it is recommended that a horizontal diamond wire line 
core hole be drilled rather than further vertical drilling. 
This would both provide additional design information prior to 
tunneling and serve as a drain. 

The problem of bad ground at the portals occasioned by 
the incompetent residual soils and colluvium as well as the 
incompetent rock formations indicates that the south slope may 
require excavation down to the competent Keefer formations 
prior to tunneling. The electrical resistivity survey would 
not offer as fine a resolution for the determination of this 
interface as would a refraction seismic survey done only at the 



199 



portals with portable equipment. Such a survey would determine 
the attitude of the contact with the Keefer much more accuratly 
than is possible using the resistivity survey alone. Three 
boreholes logged with spontaneous potential and resistivity 
logs would yield adequate correlation points between the 
Keefer and the overlying material. 



200 



APPENDIX A: 



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201 



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202 



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203 



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* 



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210 



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211 



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216 



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217 



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218 



APPENDIX B 
GLOSSARY 



The following definition of terms are drawn largely from the 
Manual of Remote Sensing (Am. Soc. Photogrammetry, 1975), Glossary 
of Geology (Am. Geological Institute, 1972), and Remote Sensing Tech- 
niques for Environmental Analysis (Estes and Senger, 1974). 

absorbed light: Light rays that are neither reflected nor transmitted 
when directed toward opaque or transparent materials. 

absorption: (1) The process by which radiant energy is absorbed and 

converted into other forms of energy. Absorption takes place only 
after the radiant flux enters a medium and thus acts only on the 
entering flux and not on the incident flux, some of which may be 
reflected at the surface of the medium. A substance which absorbs 
energy may also be a medium of refraction, diffraction, or scat- 
tering; these processes, however, involve no energy retention or 
transformation, and are to be clearly differentiated from absorption, 
(2) In general, the taking up or assimilation of one substance by 
another. See adsorption. 

absorption band: A range of wavelengths (or frequencies) in the electro- 
magnetic spectrum within which radiant energy is absorbed by a 
substance. See absorption spectrum. 

absorption line: A minute range of wavelengths (or frequencies) in the 
electromagnetic spectrum within which radiant energy is absorbed by 
the medium through which it is passing. Each line is associated 
with a particular mode of electronic excitation induced in the 
absorbing atoms by the incident radiation. See absorption spectrum, 
Fraunhofer lines, absorption band. 

absorption spectrum: The array of absorption lines and absorption bands 
which results from the passage of radiant energy from a continuous 
source through a selectively absorbing medium cooler than the 
source. See electromagnetic spectrum. The absorption spectrum is 
a characteristic of the absorbing medium, just as an emission 
spectrum is a characteristic of a radiator. An absorption spectrum 
formed by a monatomic gas exhibits discrete dark lines, whereas 
that formed by a polyatomic gas exhibits ordered arrays (bands) of 
dark lines, which appear to overlap. This type of absorption is 
often referred to as line absorption. The spectrum formed by a 
selectively absorbing liquid or solid is typically continuous in 
nature (continuous absorption). 

active microwave: Ordinarily referred to as radar, which see. 



219 



active systems: (1) A system having its own source of EMR as for ex- 
ample a radar or an ultraviolet blacklight. (2) A system that 
measures EMR that is reflected from a surface or object, and not 
produced (emitted) by the surface or object. Compare passive 
systems. 

adit: A horizontal or nearly horizontal passage driven from the surface 
for the working or unwatering of a mine. If driven through the 
hill or mountain to the surface on the opposite side it would be a 
tunnel. 

additive color process: A method for creating essentially all colors 
through the addition of light of the 3 additive color primaries 
(blue, green, and red) in various proportions through the use of 3 
separate projectors. In this type of process each primary filter 
absorbs the other 2 primary colors and transmits only about one- 
third of the luminous energy of the source. It also precludes the 
possibility of mixing colors with a single light source because the 
addition of a second primary color results in total absorption of 
the only light transmitted by the first color. 

adsorption: adherence of gas molecules or of ions or molecules in 

solutions to the surfaces of solids with which they are in contact. 
Adsorbed water in soil is held so strongly that it is resistant to 
the pull of gravity and to capillary action. 

aerial photograph, vertical: An aerial photograph made with the optical 
axis of the camera approximately perpendicular to the Earth's 
surface and with the film as nearly horizontal as is practicable. 

aerial photographs, overlapping: Two or more aerial photographs to 
which a portion of the total area projected thereon is common. 
Such photographs are used for stereoscopic studies and for making 
mosaics. Overlap may be end or forward (along the flight path) or 
side (taken during two or more parallel flights); both end and side 
overlap are customary when more than one line or strip is flown. 

albdeo: (1) The ratio of the amount of EMR reflected by a body to the 
amount incident upon it, often expressed as a percentage, as, the 
albedo of the Earth is 34 percent. (2) The reflectivity of a body 
as compared to that of a perfectly diffusing surface at the same 
distance from the Sun, and normal to the incident radiation (see 
band, albedo, reflectance). Albedo is sometimes used to mean the 
flux of the reflected radiation as, the Earth's albedo is 0.64 
calorie per square centimeter. This usage should be discouraged. 
Albedo may refer to the entire solar spectrum or merely to the 
visible portion. 



220 



alluvium: A general term for unconsolidated detrital material deposited 
during recent geologic time by a stream as a sorted or semi-sorted 
sediment. 

angle of sun: The angle of the sun above the horizon. Not only the 
quantity (lunes) of light being reflected to the aerial camera but 
also the spectral quality, are influenced by sun-angle. Also 
called sun elevation, sun elevation angle. 

o 

angstrom (A or A): Unit of measurement, 10" '^ m. 

annotated photograph: A photograph on which planimetric, hypsographic, 
geologic, cultural, hydrographic, or vegetation information has 
been added to identify, classify, outline, clarify, or describe 
features that would not otherwise be apparent in examination of an 
unmarked photograph. 

antenna, synthetic aperature (radar): The effective antenna produced by 
storing and comparing the doppler signals received while the air- 
craft travels along its flight path. This synthetic antenna (or 
array) is many times longer than the physical antenna, thus sharp- 
ening the effective beam width and improving azimuth resolution. 

anticline: A fold, the core of which contains the stratigraphically 
older rocks: it is convex upward. Ant: syncline. 

azimuth: The direction of a line given as an angle measured clockwise 
from a reference direction, usually north. (2, radar): Direction 
at right angles to the antenna beam. In side-looking radar, the 
direction parallel to ground track. 

band: See spectral band 

band-pass filter: (2) A wave filter that has a single transmission band 
extending from a lower cutoff frequency greater than zero to a 
finite upper cutoff frequency. 

bandwidth: (1) In an antenna, the range of frequencies within which its 
performance, in respect to some characteristic, conforms to a 
specified standard. (2) In a wave, the least frequency interval 
outside of which the power spectrum of a time- varying quantity is 
everywhere less than some specified fraction of its value at a 
reference frequency. (3) The number of cycles per second between 
the limits of a frequency band. Sense 2 permits the spectrum to be 
less than the specified fraction within the interval. Unless 
otherwise stated, the reference frequency is that at which the 
spectrum has its maximum value. 

basin range: (1) A relatively long and narrow mountain range that owes 
its present elevation and structural form mainly faulting and 
tilting of strata and that is isolated by alluvium-filled basins or 

221 



valleys. (2) A tilted fault block— Etymol : from the Great Basin, a 
region in SW U.S. characterized by fault-block mountains. 

bearing: Direction of a line measured as an acute angle from a refer- 
ence meridian. Compare with azimuth. 

blackbody, black body: An ideal emitter which radiates energy at the 
maximum possible rate per unit area at each wave-length for any 
given temperature. A blackbody also absorbs all the radiant evergy 
incident upon it. No actual substance behaves as a true blackbody 
although platinum black and other soots rather closely approximate 
this ideal. In accordance with Kirchhoff's law, a blackbody not 
only absorbs all wavelengths, but emits at all wavelengths and does 
so with maximum possible intensity for any given temperature. 

black-body radiation: The electromagnetic radiation emitted by an ideal 
black body; it is the theoretical maximum amount of radiant energy 
of all wavelengths which can be emitted by a body at a given temp- 
erature. The spectral distribution of black-body radiation is 
described by Planck's law and related radiation laws. If a yery 
tiny opening is made into an otherwise completely enclosed space 
(hohlraum), the radiation passing out through this hole when the 
walls of the enclosure have come to thermal equilibrium at some 
temperature will closely approximate ideal black-body radiation for 
that temperature. 

brute force: A sidelooking radar system that transmits and receives 
from a long physical antenna to narrow the beamwidth and increase 
azimuth resolution; the received returned EMR is used directly to 
produce an image. Compare synthetic aperature. 

camera, metric: A specially constructed and calibrated camera used to 
olDtain geometrically accurate photographs for use in photogram- 
metric instruments. 

camera, multiband: A camera that exposes different areas of one film, 
or more than one film, through one lens and a beam splitter, or two 
or more lenses equipped with different filters, to provide two or 
more photographs in different spectral bands. 

case hardening: The process by which the surface of a porous rock (esp. 
tuff and certain sandstones) is coated with a cement or desert 
varnish formed by evaporation of mineral -bearing solutions. Adj : 
case-hardened. Also spelled: casehardening. 

colluvium: (1) A general term applied to any loose, heterogeneous, and 
incoherent mass of soil material or rock fragments deposited chiefly 
by mass-wasting, usually at the base of a steep slope or cliff; 
e.g. talus, cliff debris, and avalanche material. (2) Alluvium 
deposited by unconcentrated surface run-off or sheet erosion, 
usually at the base of a slope. 

222 



color balance: The proper intensities of colors in a color print, 

positive transparency, or negative, that give a correct reproduc- 
tion of the gray scale (as faithful as can be achieved by photo- 
graphic representation of the true colors of a scene). 

color composite (multiband photography): A color picture produced by 
assigning a color to a particular spectral band. In LANDSAT, 
ordinarily blue is assigned to band 1 or 4 (^500 to 600 nm) , green 
to band 2 or 5 (%6G0 to 700 nm) , and red to band 3 (^^700 nm to 
1 ym) or 7 ('^^SOO nm to 1.1 ym) , to form a picture closely approxi- 
mating a col or- infrared photograph. 

contact: A plane or irregular surface between two different types or 
ages or rocks. 

contact print: A print made from a negative or a diapositive in direct 
contact with sensitized material. 

coverage, stereoscopic: Aerial photographs taken with sufficient 
overlap to permit complete stereoscopic examination. 

cut-off filter: A filter, shaped to remove unwanted radiation, either 
above (low-pass) or below (high-pass) a desired band of radiation. 

densitometer: An instrument for the measurement of optical density 

(density of the silver deposit) (photographic transmission, photo- 
graphic reflection, visual transmission, etc.) of a material, 
generally of a photographic image. There are many varieties, but 
all are alike in providing means for reducing the intensity of a 
standard light constantly until it matches an identical beam of 
light which has passed through the material being measured. See 
also microdensitometer. 

depression angle: (1, general) any angle measured from the horizontal 
to an object below the observer. (2, radar) The angle formed by 
the horizontal plane and the line of the radar beam to a ground 
feature. 

desert varnish: A thin, dark, hard, shiny or glazed iridescent (red, 
brown, black) film, coating, stain, or polish composed of iron 
oxide accompanied by traces of manganese oxide and silica, formed 
in desert regions after long exposure upon the surfaces of pebbles, 
boulders, and other rock fragments, as well as upon the cracked 
walls of ledges and other rock out-crops; it is believed to be 
caused by exudation of mineralized solutions from within and dep- 
osition by evaporation on the surface. A similar appearance pro- 
duced by wind abrasion is properly known as desert polish. Syn: 
desert patina; desert lacquer; desert crust; desert rind. 



223 



diapositive: A positive image on a transparent medium such as glass or 
film; a transparency. The term originally was used primarily for a 
transparent positive on a glass plate used in a plotting instrument, 
a projector, or a comparatory, but now is frequently used for any 
positive transparency. 

dike: A tabular igneous intrusion that cuts across the planar structures 
of the surrounding rock. 

dip: The angle at which a stratum or any planar feature is inclined 
from the horizontal. 

disconformity: An unconformity in which the bedding planes above and 
below the break are essentially parallel, indicating a significant 
interruption in the orderly sequency of sedimentary rocks, gener- 
ally by a considerable interval of erosion (or sometimes of non- 
depostion), and usually marked by a visible and irregular or uneven 
erosion surface of appreciable relief; e.g. an unconformity in 
which the older rocks remained essentially horizontal during ero- 
sion or during simple vertical rising and sinking of the crust 
(without tilting or faulting). The tendency is to apply the term 
to breaks represented elsewhere by rock units of formation rank. 

displacement: Any shift in the position of an image on a photograph 
which does not alter the perspective characteristics of the photo- 
graph (i.e. shift due to tilt of the photograph, scale change in 
the photograph, and relief of the objects photographed). 

dissected: Cut by erosion into hills and valleys or into flat upland 
areas separated by valleys. 

diurnal (thermal) wave: The daily temperature rise of the surface 
soils, under the heating of the sun, progresses downward as a 
heavily dampened wave which dies out about 30 cm below the surface. 
Below this point relatively constant daily temperatures may be 
experienced. 

electromagnetic radiation (EMR): Energy propagated through space or 
through material media in the form of an advancing interaction 
between electric and magnetic fields. The term radiation, alone, 
is used commonly for this type of energy, although it actually has 
a broader meaning. Also called electromagnetic energy. See 
electromagnetic spectrum. 

electromagnetic spectrum: The ordered array of known electromagnetic 
radiations extending from the shortest cosmic rays, through gamma 
rays. X-rays, ultraviolet radiation, visible radiation, infrared 
radiation, and including microwave and all other wavelengths of 
radio energy. 



224 



emission: (1) With respect to EMR, the process by which a body emits 
EMR usually as a consequence of its temperature only. Compare 
reflection, transmission. See emissitivity. 

emission spectrum: The array of wavelengths and relative intensities of 
EMR emitted by a given radiator. 

emissivity: A ratio relating the amount of energy given off by an 

object to the amount given off by a "black body" at the same tem- 
perature, and normally expressed as a real positive number between 
and 1. 

erosion: (1) The general process or the group of processes whereby the 
earthy and rocky materials of the Earth's crust are loosened, 
dissolved, or worn away, and simultaneously removed from one place 
to another by natural agencies that include weathering, solution, 
corrasion, and transportation, but usually exclude mass-wasting; 
specif, the mechanical destruction of the land and the removal of 
material (such as soil) by running water (including rainfall), 
waves and currents, moving ice or wind. The term is sometimes 
restricted by excluding transportation (in which case "denudation" 
is the more general term) or weathering (thus making erosion a 
dynamic or active process only). (2) An instance or product, or 
the combined effects, of erosion. 

exposure: (1) The total quantity of light received per unit area on a 
sensitized plate or i^ilm; may be expressed as the product of the 
light intensity and the exposure time, in units of (for example) 
meter-candle-seconds or watts per square meter. (2) The act of 
exposing a light-sensitive material to a light source. (3 geol.) 
A continuous area in which a rock formation or geological structure 
is visible, either naturally or artificially, and is unobscured by 
soil, vegetation, water or the works of man. 

fault: A fracture surface or zone in rock along which a measureable 
displacement has taken place. 

filter: (1, noun) Any material which, by absorption or reflection, 
selectively modifies the radiation transmitted through an optical 
system. Such a filter may operate by polarization, scattering, 
etc., and may also be electronic. Also called wave filter. The 
filter usually is interposed between the film and the scene being 
photographed, but it may form part of the film itself. (2, verb) 
To remove a certain component or components of EMR, usually be 
means of a filter, although other devices may be used. 

flatiron: One of a series of short, triangular-shaped hogbacks ter- 
minating a spur or ridge on the flank of a mountain, having a 
narrow apex at the top and a broad base below, resembling (when 
viewed from the side) a huge flatiron standing on its heel; it 

225 



usually consists of a plate of steeply inclined resistant rock 
adhering to the dip slope. 

flight altitude: The vertical distance above a given datum, usually 
mean sea level, of an aircraft in flight or during a specified 
portion of a flight. In aerial photography, when the datum is mean 
ground level of the area being photographed, this distance is 
called flight height or sometimes obsolute altitude, (see also, 
above mean terrain, AMI) 

flight strip: A succession of overlapping aerial photographs taken 
along a single course. 

focal length, calibrated: An adjusted value of the equivalent focal 
length, computed to equalize the positive and negative values of 
distortion over the entire field used in the aerial camera. Also 
stated as the distance along the lens axis from the interior per- 
spective center to the image plane; the interior center of the 
perspective being selected so as to equalize the positive and 
negative values of lens distortion over the field. The calibrated 
focal length is used when determining the setting of diapositives 
in plotting instruments and in photogrammetric computations based 
on linear measurements on the negative, such as those made with a 
precision comparator. 

fold: (struc. geol ) . A curve or bend of a planar structure such as 
rock strata, bedding planes, foliation, or cleavage. A fold is 
usually a product of deformation, although its definition is 
descriptive and not genetic and may include primary structures. 

foliation: (struc. geol). A general term for a planar arrangement of 
textural or structural features in any type of rock, e.g., cleavage 
in slate or schistosity in a metamorphic rock. It is most commonly 
applied to metamorphic rock. 

footwall: The underlying side of a fault. Cf: hanging wall. 

fracture: A surface along which loss of cohesion has taken place. That 
is in geology, a general term for any break in a rock. A fracture 
along which no displacement has occurred is a joint, while one 
along which the rock has been displaced is a fault. 

Fraunhofer line(s): Dark line(s) in the absorption spectrum of solar 
radiation due to absorption by gases in the outer portions of the 
Sun and in the Earth's atmosphere. Fraunhofer lines are designated 
by letters, as the K-line, or by wavelength, as the 4046-anstrom 
1 ine of iron. 

gneiss: A foliated rock formed by regional metamorphism in which bands 
or lenticles of granular minerals alternate with bands and lenticles 

226 



in which minerals having flaky or elongate prismatic habits pre- 
dominate. Generally less than 50% of the minerals show preferred 
parallel orientation. Although a gneiss is commonly feldspar- and 
quartz-rich, the mineral composition is not an essential factor in 
its definition (American usage). Varieties are distinguished by 
texture (e.g. augen gneiss), characteristic minerals (e.g. horn- 
blende gneiss), or general composition and/or origins (e.g. granite 
gneiss). 

gray body: A radiating surface whose radiation has essentially the same 
spectral energy distribution as that of a blackbody at the same 
temperature, but whose emissive power is less. Its absorptivity is 
nonselective. Also spelled grey body. 

gray scale: A monochrome strip of shades ranging from white to black 
with intermediate shades of gray. The scale is placed in a setup 
for a color photograph and serves as a means of balancing the 
separation negatives and positive dye images. 

Greenwich mean time (abbr GMT): Local mean time at the Greenwich meridi- 
an; the arc of the celestial equator, or the angle at the celestial 
pole, between the lower branch of the Greenwich celestial meridian 
and the hour circle of the mean sun, measured westward from the 
lower branch of the Greenwich celestial meridian through 24 hours; 
Greenwich hour angle of the mean sun, expressed in time units, plus 
12 hours. Also called universal time, Z-time. Mean time reckoned 
from the upper branch of the Greenwich meridian is called Greenwich 
astronomical time. 

ground truth (jargon): Term coined for data/information obtained on 
surface/subsurface features to aid in interpretation of remotely 
sensed data. A vague, misleading term suggesting that the truth 
may be found on the ground. Ground data and ground information are 
preferred terms. 

ground water: (a) That part of the subsurface water that is the zone of 
saturation, including underground streams. See also phreatic 
water. Syn: plerotic water, (b) Loosely, all subsurface water 
(excluding internal water) as distinct from surface water--Also 
spelled, groundwater, ground-water. 

hanging wall: The overlying side of a fault. Dv: footwall. 

Hertz (abbr. Hz): The unit of frequency, cycles per second. 

hydrothermal alteration: Alteration of rocks or minerals by the reac- 
tion of hydrothermal water with preexisting solid phases. 

igneous: Said of a rock or mineral that solidified from molten or 

partly molten material, i.e. , from a magma; also, applied to pro- 
cesses leading to, related to, or resulting from the formation of 

227 



such rocks. "Igneous" rocks consitute one of the three main classes 
into which all rocks are divided (i.e. igneous, metamorphic, sedi- 
mentary), Etymol : Latin ignis, "fire". 

illumination: The intensity of light striking a unit surface is known 
as the specific illumination of luminous flux. It varies directly 
with the intensity of the light source and inversely as the square 
of the distance between the illuminated surface and the source. It 
is measured in a unit called the lux. The total illumination is 
obtained by multiplying the specific illuminiation by the area of 
the surface when the light strikes. The unit of total illumination 
is the lumen. 

image: (1) The counterpart of an object produced by the reflection of 
refraction of light when focused by a lens or mirror. 

image: (2) The recorded representation of an object produced by optical, 
electro optical, optical mechanical, or electronic means. It is 
generally used when the EMR emitted or reflected from a scene is 
not directly recorded on film. 

image enhancement: The manipulation of image density to more easily see 
certain features of the image. 

imagery: The products of image-forming instruments (analogous to photo- 
graphy). 

infrared (abbr. IR): Pertaining to or designating the portion of the EM 
spectrum with wavelengths just beyond the red end of the visible 
spectrum, such as radiation emitted by a hot body (see infrared 
radiation) . 

infrared line scanner: See scanning radiometer. 

infrared photographic: (1) Pertaining to or designating the portion of 
the EM spectrum with wavelengths just beyond the red end of the 
visible spectrum, such as radiation emitted Ny a hot body (over 
500° C); generally defined as from 0.7 to about 1.0 mm, or the 
useful limits of film sensitivities. 

infrared radiation: EMR in the wavelength interval from about .75 mm to 
1 mm. Also called long wave radiation. At its lower limit, in- 
frared radiation spectrum is bounded by visible radiation, and on 
its upper limit by microwave radiation. 

intrusive body: (ign) the igneous rock mass formed by the emplacement 
of magma in pre-existing rock. 

joint: A surface or actual or potential fracture or posting in a rock, 
without displacement; the surface is usually plane and often occurs 
with parallel joints for form part of a joint set. 

228 



K-band: A frequency band used in radar extending approximately from 
10.9 gigahertz to 36 gigahertz. 

large-scale: (1) Aerial photographs with a representative fraction of 
1:500 to 1:10,000. (2) Maps with a representative fraction (scale) 
greater than 1 :100,000. 

lineament: (photo). Any line, on an aerial photograph, that is struc- 
turally controlled, including any alignment of separate photographic 
images such as stream beds, trees, or bushes that are so controlled. 
The term is widely applied to lines representing beds, lithologic 
horizons, mineral bandings, veins, faults, joints, unconformities, 
and rock boundaries (Allum, 1966, p. 31). 

lineament: (tect). Straight or gently curved, lengthy features of the 
Earth's surface, frequently expressed topographically as depres- 
sions or lines of depressions; these are prominent on relief models, 
high-altitude air photographs, and radar imagery. Their meaning 
has been much debated; some certainly express valid structural 
features, such as faults, aligned volcanoes, and zones of intense 
jointing with little displacement, but the meaning of others is 
obscure, and their origins may be diverse, or purely accidential. 
Syn: linear. 

linear: Arranged in a line or lines, as a linear dike swarm. It is a 
one-dimensional arrangement, in contrast to the two-dimensional 
planar arrangement. 

lithology: (1) The description of rocks, esp. sedimentary elastics and 
esp. in hand specimen and in outcrop, on the basis of such char- 
acteristics as color, structures, mineralogic composition, and 
grain size. As originally used, "lithology" was essentially syn- 
onymous with petrography as currently defined. (2) The physical 
character of a rock Adj ; lithologic. 

medium scale: (1) Aerial photographs with a representative fraction of 
1:12,000 to 1:30,000. (2) Maps with a representative fraction 
(scale) of 1:100,000 to 1:1,000,000. 

metamorphic: Pertaining to the process of metamorphism or to its re- 
sults, n. A metamorphic rock, usually used in the plural, e.g. 
"the metamorphics" of an area. 

metasediments: (1) A sediment or sedimentary rock which shows evidence 
of having been subjected to metamorphism. (2) A metamorphic rock 
of sedimentary origin. 

Microdensitometer: A special form of densitometer for reading densities 
in very small areas; used for studying astronomical images, spectro- 
scopic records, and for measuring image edge gradients and grain- 
iness in films. 

229 



multiband system: A system for simultaneously observing the same (small) 
target with several filtered bands, through which data can be 
recorded. Usually applied to cameras, may be used for scanning 
radiometers which utilize dispersant optics to split wavelength 
bands apart for viewing be several filtered detectors. See spectra 
zonal. 

multi-lens camera: (1) A camera having two or more lenses pointing at 
the same taret, which when used with different film/filter com- 
binations, produces multiband photographs. (2) A camera having two 
or more lenses pointed at an angle to one another, and taking two 
or more overlapping pictures, simultaneously. 

mul ti spectral : Generally used for remote sensing in two or more spectral 
bands, such as visible and IR. 

mul ti spectral (line) scanner: A remote sensing device which operates on 
the same principle as the infrared scanner except that it is capable 
of recording data in the ultraviolet and visible portions of the 
spectrum as well as the infrared. See scanning radiometer. 

nanosecond (abbr. nsec): A prefix meaning multiplied by 10"^ second. 
Formerly called millimicrosecond. 

near infrared: The preferred term for the shorter wavelengths in the 

infrared region extending from about 0.7 micrometers (visible red), 
to around 2 or 3 micrometers (varying with the author). The longer 
wavelength end grades into the middle infrared. The term really 
emphasizes the radiation reflected from plant materials, which 
peaks around 0.85 micrometers. It is also called solar infrared, 
as it is only available for use during the daylight hours. 

negative: (1) A photographic image on film, plate, or paper, in which 
the tones are reversed. (2) A film, plate, or paper containing 
such a reversed image. 

nonconformity: (1) An unconformity developed between sedimentary rocks 
and older rocks (plutonic igneous or massive metamorphic rocks) 
that had been exposed to erosion before the overlying sediments 
covered them. The restriction of the term to this usage was pro- 
posed by Dunbar & Rodgers (1957, p. 119). Although the term is 
"well known in the classroom", it is "not commonly used in prac- 
tice" (Dennis, 1967, p. 160). Syn. heterolithic unconformity. (2) 
A term that formerly was widely, but now less commonly, used as a 
syn. of angular unconformity, or as a generic term that includes 
angular unconformity--term proposed by Pirsson (1915, p. 291-293). 

normal fault: A fault in which the hanging wall appears to have moved 
downward relative to the footwall. The angle of the fault is 
usually 45-90°. There is dip separation but there may or may not 
be dip slip. Cf: thrust fault. Syn: gravity fault: normal slip 
fault; slump fault. 

230 



panchromatic: Used for films that are sensitive to broad band (e.g., 
entire visible part of spectrum) EMR, and for broad band photo- 
graphs. 

passive system: A sensing system that detects or measures radiation 
emitted by the target. Compare active system. 

photomap: A single photo, composite, or mosaic showing coordinates and 
marginal information: normally reproduced in quantity. 

polarization: (1) The direction of the electric vector in an EM wave 

(light or radio). A wave is said to be unpolarized if the direction 
of the electric vector is randomly disturbed (has random orienta- 
tion), so that the direction at any instant cannot be predicted. 
Natural radiation from gases is usually unpolarized, but radiation 
from manmade sources is always polarized in radio wavelengths and 
often polarized even in optical wavelengths. Because reflection is 
different for different polarizations, reflected waves are always 
polarized to some extent even though they may be originally emitted 
in unpolarized form. Waves may be plane-polarized, or linearly 
polarized, in which case the electric vector is in the same direc- 
tion at all points in the wave. They may also be circularly or 
elliptically polarized, in which case the direction of the electric 
vector at some point changes with time (circular) or both direction 
and amplitude change in a relative manner (elliptical). (2) With 
respect to particles or crystals in an electric field, the displace- 
ment of charge centers from their normal positions caused by the 
force of the electric field. 

polarizing filter: A filter which passes light waves vibrating in one 
polarization direction only. Used over camera lenses to cut down 
or remove, rays of any or all other polarization di recti on (s) when 
they may constitute objectionable reflections from glass, water, or 
other highly reflecting surfaces. 

positive: (1) A photographic image having approximately the same ren- 
dition of light and shade as the original subject. (2) A film, 
plate, or paper containing such an image. 

prime meridian: An arbitrary meridian selected as a reference line 
having a longitude of zero degrees and used as the origin from 
which other longitudes are reckoned east and west to 180 degrees; 
specif, the Greenwich meridian. Local or national prime meridians 
are occasionally used. Syn: aero meridian; initial meridian; first 
meridian. 

pyroclastics: Pertaining to clastic rock material formed by volcanic 
explosion or aerial expulsion from a volcanic vent; also, pertain- 
ing to rock texture of explosive origin. It is not synonymous with 
the adjective "volcanic". 



231 



quartzite: (met). A metamorphic rock consisting mainly of quartz and 
formed by recrystallization of sandstone or chert by either re- 
gional or thermal metamorphism; meta-quartzite. 

quartzite: (sed). A \/ery hard but unmetamorphosed sandstone consisting 
chiefly of quartz grains that have been so completely and solidly 
cemented (diagenetically) with secondary silica that the rock 
breaks across or through the individual grains rather than around 
them; an orthoquartzite. The cement grows in optical and crystal- 
lographic continuity around each quartz grain, thereby tightly 
interlocking the grains as the original pore spaces are completely 
filled with secondary enlargements developed on the grains. 
Skolnick (1965) believes that most sedimentary quartzites are 
compacted sandstones developed by pressure solution of quartz 
grains. 

radar: Acronym for radio detection and ranging. A method, system, or 
technique, including equipment components, for using beamed, re- 
flected, and timed EMR to detect, locate, and (or) track objects, 
to measure altitude and to acquire a terrain image. In remote 
sensing of the Earth's or a planetary surface, it is used for 
measuring, and often, mapping the scattering properties of the 
surface. 

radar, brute force: A radar imaging system employing a long physical 
antenna to achieve a narrow beam-width for improved resolution. 

radar, synthetic aperature (SAR): A radar in which a synthetically long 
apparent or effective aperture is constructed by integrating mul- 
tiple returns from the same ground cell, taking advantage of the 
Doppler effect to produce a phase history film or tape that may be 
optically or digitally processed to reproduce an image. 

radiation: The emission and propagation of energy through space or 

through a material medium in the form of waves; e.g., the emission 
and propagation of EM waves, or of sound and elastic waves. The 
process of emitting radiant energy. 

radiometer: An instrument for quantitively measuring the intensity of 
EMR in some band of wavelengths in any part of the EM spectrum. 
Usually used with a modifier, such as IR radiometer or microwave 
radiometer. Most radiometers measure the difference between the 
source radiation incident on the detector and a radiant energy 
(blackbody) reference. Comparison between the two is often 
achieved by mechanically interposing a reflective chopper, so 
that both sources can be viewed consecutively by the same detector, 
or by electrically switching, as in a microwave radiometer. 



232 



reflectance: A measure of the ability of a body to reflect light or 

sound. The reflectance of a surface depends on the type of surface, 
the wavelength of the illumination, and the illumination and view- 
ing angles. 

remote sensing: In the broadest sense, the measurement of acquisition 
of information of some property of an object or phenomenon, by a 
recording device that is not in physical or intimate contact with 
the object of phenomenon under study; e.g., the utilization at a 
distance (as from aircraft, spacecraft, or ship) of any device and 
its attendant display for gathering information pertinent to the 
environment, such as measurements of force fields, electromagnetic 
radiation, or acoustic energy. The technique employs such devices 
as the camera, lasers, and radio frequency receivers, radar systems, 
sonar, seismographs, gravimeters, magnetometers, and scintillation 
counters. (2) The practice of data collection in the wavelengths 
from ultraviolet to radio regions. This restricted sense is the 
practical outgrowth from airborne photography. Sense 1 is pre- 
ferred and thus includes regions of the EM spectrum as well as 
techniques traditionally considered as belonging to conventional 
geophysics. 

resolution: The ability of an entire remote sensor system, including 
lens, antennae, display, exposure, processing, and other factors, 
to render a sharply defined image. It may be expressed as line 
pairs per millimeter or meters, or in many other manners. In 
radar, resolution usually apples to the effective radar, resolution 
usually applies to the effective beamwidth and range measurement 
width, often defined as the half-power points. For infrared line 
scanner scanners the resolution may be expressed as the instanteous 
field-of-view, which see. Resolution also may be expressed in 
terms of temperature or other physical property being measured. 

reststraheln or (residual) rays: An almost metallic reflection occurs 
in transparent materials where either the refractive index (n) is 
high, or when the absorption coefficient (K) is large. These 
narrow bands of reflectance are called the residual rays. Such 
wavelength regions show higher reflectance (and lower emittance) 
than elsewhere and provide chemical and structural information 
which may be remotely sensed. 

reverse fault: Generally considered a fault with a dip between 45° and 
vertical in which the hanging wall has moved upward in relation to 
the footwall. In a broad sense thrust faults are also reverse 
faults. 

scale: (1) The full range of tones of which a photographic paper is 

capable of reproducing is called the scale of the paper, it is also 
termed dynamic range, which see. (2) The ratio of a distance on a 
photograph or map to its corresponding distance on the ground. The 

233 



scale of a photograph varies from point to point because of dis- 
placements caused by tilt and relief, but is usually taken as f/H 
where f is the principal distance (focal length) of the camera and 
H is the height of the camera above mean ground elevation. Scale 
may be expressed as a ratio, 1:24,000; a representative fraction, 
1/24,000; or an equivalence, 1 in. = 2,000 ft. See also represen- 
tative fraction. 

scanners: (1) Any device that scans, and by this means produced an 

image. See scanning radiometer. (2) A radar set incorporating a 
rotatable antenna, or radiator element, motor drives, mounting, 
etc. for directing a searching radar beam through space and im- 
parting target information to an indicator. 

scanning radiometer: A radiometer, which by the use of a rotating or 

oscillating plane mirror, can scan a path normal to the movement of 
the radiometer. The plane mirror may move in various patterns - 
arcs, circles, lines. The mirror directs the incoming radiation to 
a detector, which converts it into a electrical signal. This 
signal is amplified to stimulate a device such as a tape recorder, 
or glow tube or CRT that can be photographed to produce a picture. 
When the system is moved forward at velocity V and at altitude H, a 
suitable V/H ratio may be established, so that consecutive scans 
are just touching. This is often called an IR-imager, but is only 
so restricted because of the optical materials used, all-reflective 
optics being as useful in the UV and visible regions. They may all 
be single-or multiple-band. 

scarp: (1) A line of cliffs produced by faulting or by erosion. The 
term is an abbreviated form of escarpment, and the two terms com- 
monly have the same meaning, although "scarp" is more often applied 
to cliffs formed by faulting. (2) A relatively steep and straight, 
cliff-like face or slope of considerable linear extent, breaking 
the general continuity of the land by separating level or gently 
sloping surfaces lying at different levels, as along the margin of 
a plateau, mesa, terrace, or bench. A scarp may be of any height. 
The term should not be used for a slope of highly irregular outline. 
(3) beach scarp. (4) A steep surface on the undisturbed ground 
around the periphery of a landslide, caused by movement of slide 
material away from the undisturbed ground; also, a similar but 
smaller feature on the disturbed material, produced by differential 
movements within the sliding mass. 

schist: A strongly foliated crystalline rock formed by dynamic meta- 
morphism which can be readily split into thin flakes or slabs due 
to the well developed parallelism of more than 50% of the minerals 
present, particularly those of lamellar or elongate prismatic 
habit, e.g. mica, hornblende. The mineral composition is not an 
essential factor in its definition (American usage) unless specifi- 
cally included in the rock name, e.g. quartz-muscovite schist. 



234 



Varieties may also be based on general composition, e.g. calc- 
silicate schist, amphibolite schist, or on texture, e.g. spotted 
schist. 

sediment: (1) Solid fragmental material, or a mass of such material, 
either inorganic or organic, that originates from weathering of 
rocks and is transported by, suspended in, or deposited by, air, 
water, or ice, or that is accumulated by other natural agents, such 
as chemical precipitation from solution or secretion by organisms, 
and that forms in layers on the Earth's surface at ordinary tem- 
peratures in a loose, unconsolidated form; e.g., sand, gravel, 
silt, mud, till, loess, alluvium. (2) Strictly, solid material 
that has settled down from a state of suspension in a liquid — in 
the singular, the term is usually applied to material held in 
suspension in water or recently deposited from suspension, in the 
plural, the term is applied to all kinds of deposits, and refers to 
essentially unconsolidated materials; the plural usage as applied 
to consolidated sedimentary rocks should be avoided (USGS, 1958, 
p. 86) Cf: deposit. 

sedimentary: adj. (1) Pertaining to or containing sediment; e.g., a 
"sedimentary deposit" or a "sedimentary complex." (2) Formed by 
the deposition of sediment (e.g., a "sedimentary clay"), or per- 
taining to the process of sedimentation (e.g., "sedimentary vol- 
canism"). — n. A sedimentary rock or deposit. 

sensor: Any device which gathers energy EMR or other and presents it in 
a form suitable for obtaining information about the environment. 
Passive sensors, such as thermal infrared and microwave, utilize 
EMR produced by the surface or object being sensed. Active sensors, 
such as radar, supply their own energy source. Aerial cameras use 
natural or artifically produced EMR external to the object or 
surface being sensed. 

serpentine: A group of common rock-forming minerals having the formula: 
(MG,Fe)3Si205(0H)4. Serpentines have a greasy or silky luster, a 
slightly soapy feel, and a tough, conchoidal fracture; they are 
usually compact but may be granular or fibrous, and are commonly 
green, greenish yellow, or greenish gray (sometimes brown, black, 
or white) and often veined or spotted with red, green, and white. 
Serpentines are always secondary minerals, derived by alteration of 
magnesium-rich silicate minerals (esp. olivines), and are found in 
both igneous and metamorphic rocks. 

sidelooking radar: An all weather, day/night remote sensor which is 

particularly effective in imaging large areas of terrain. It is an 
active sensor, as it generates its own energy which is transmitted 
and received to produce a photo-like picture of the ground. Also 
referred to as sidelooking airborne radar. 



235 



signature: Any characteristic or series of characteristics by which a 
material may be recognized. Used in the sense of spectral signa- 
ture, as in photographic (color reflectance). 

signature analysis techniques: Techniques which use the variation in 
the spectral reflectance or emittance of objects as a method of 
identifying the objects. 

sinkhole: A geomorphic feature produced where rocks such as salt, 

gypsum, or limestone have been locally dissolved away. The earth 

may sink and form a cup-shaped basin to which this name is given. 
Syn: sink; lime sink; limestone sink; leach hole. 

spectral band: An interval in the electromagnetic spectrum defined by 
two wavelengths, frequencies, or wave numbers. 

spectral signature: Quantitative measurement of the properties of an 
object at one or several wavelength intervals. 

spectrometer: A device to measure the spectral distribution of EMR. 
This may be achieved by a dispersive prism, grating, circular 
interference filter with a detector placed behind a slit. If one 
detector is used, the dispersive element is moved as to sequen- 
tially pass all dispersed wavelengths across the slit. In an 
inteferometer-spectometer, on the other hand, all wavelengths are 
examined all the time, the scanning effect being achieved by rapidly 
oscillating two, partly reflective, (usually parallel) plates so 
that interference fringes are produced. A Fourier transform is 
required to reconstruct the spectrum. Also called spectroradiometer, 

spectrum: (1) In physics, any series of energies arranged according to 
wavelength (or frequency). (2) The series of images produced when 
a beam of radiant energy is subject to dispersion. A rainbow- 
colored band of light is formed when white light is passed through 
a prism or a diffraction grating. This band of colors results from 
the fact that the different wavelengths of light are bent in vary- 
ing degrees by the dispersing medium and is evidence of the fact 
that white light is composed of colored light of various wave- 
lengths. 

standard meridian: (1) The meridian used for determining standard time. 
(2) A meridian of a map projection, along which the scale is as 
stated. 

stereogram: A stereo pair of photos or drawings correctly orientated 
and permanently mounted for stereoscopic examination. 

stereo pair: A pair of photos which overlap an area and are suitable 
for stereoscopic examination. 



236 



stereoscope: A binocular optical instrument for assessing the observer 
to view two properly oriented photographs or diagrams to obtain the 
mental impression of a three-dimensional model. 

stereoscopic image: That mental impression of a three-dimensional 
object which results from stereoscopic vision (stereviewing) . 

stereo triplet: A series of three photos, the end members of which 

overlap sufficiently on the central one to provide complete stereo- 
scopic coverage for the latter. 

stereoscopic vision (stereo vision): Binocular vision which enables the 
observer to view an object simultaneously from two different per- 
spectives (as two photographs taken from different camera stations) 
to obtain the mental impression of a three-dimensional model. 

strike: The direction or bearing of a horizontal line in the plane of 
an inclined stratum, joint, fault or other structural plane. 

structure: The general disposition, attitude, arrangement, or relative 
positions of the rock masses of a region or area; the sum total of 
the structural features of an area, consequent upon such deforma- 
tional processes as faulting, folding, and igneous intrusion. 

subtractive color process: A method of creating essentially all colors 
through the subtraction of light of the 3 subtractive color pri- 
maries (cyan, magenta and yellow) in various proportions through 
use of a single white light source. 

syncline: A fold, the core of which contains the stratigraphically 
younger rocks; it is concave upward. Ant. anticline. 

talus: (1) talus slope. (2) Rock fragments of any size or shape 

(usually coarse and angular) derived from and lying at the base of 
a cliff or very steep, rocky slope. Also, the outward sloping and 
accumulated heap or mass of such loose broken rock, considered as 
a unit, and formed chiefly by gravitational falling, rolling or 
sliding. 

target: (1) The distinctive marking or instrumentation of a ground 

point to aid in its identification on a photograph. In photogram- 
metry, target designates a material marking so arranged and placed 
on the ground as to form a distinctive pattern over a geodetic or 
other control-point marker on a property corner on line, or at the 
position of an identifying point above an underground facility or 
feature. (2) In radar, an object returning a radar echo to the 
receiver. 

tectonic: Said of or pertaining to the forces involved in, or the 

resulting structures or features of, tectonics. Syn; geotectonic. 



237 



thermal anomaly: A pattern of thermal energy distribution which appears 
anomalous relative to adjoining areas. If linear, these patterns 
can be termed thermal linears, in the same context as structural 
linears. 

thermal band: A general term for middle- infrared wavelengths which are 
transmitted through the atmosphere window at 8-13 micrometers. 
Occasionally also used for the windows around 3-6 micrometers. 

thermal inertia: Sometimes referred to as the thermal contact coeffi- 
cient, it is a measure of the rate of heat transfer and is the 
product of thermal conductivity and thermal capacity. The recip- 
rocal is often used instead, and is termed the "thermal parameter." 
Sometimes called conductive capacity. 

thermal infrared: The preferred term for the middle wavelength ranges 
of the IR region, extending roughly from 3 micrometers at the end 
of the near infrared, to about 15 to 20 micrometers where the far 
infrared commences. In practice the limits represent the envelope 
of energy emitted by the earth behaving as a greybody with a sur- 
face temperature around 290°K (27°C). Seen from any appreciable 
distance, the radiance envelope has several brighter bands corre- 
sponding to windows in the atmospheric absorption bands. The 
thermal band most used in remote sensing extends from 8-13 micro- 
meters. 

thrust fault: A fault with a dip of 45° or less in which the hanging 
wall appears to have moved upward relative to the footwall. Hori- 
zontal compression rather than vertical displacement is its char- 
acteristic features. Cf; normal fault. Syn. reverse fault; reverse 
slip fault; thrust slip fault; thrust. Partial syn: overthrust; 
contraction fault; overlap fault. 

tuff: A compacted phyroclastic deposit of volcanic ash and dust that 
may or may not contain up to 50% sediments such as sand or clay. 
The term is not to be confused with tufa. Adj ; tuffaceous. 

unconformity: (1) A substantial break or gap in the geologic record 
where a rock unit is overlain by another that is not next in 
stratigraphic succession, such as an interruption in the continuity 
of a depositional sequence of sedimentary rocks or a break between 
eroded igneous rocks and younger sedimentary strata. It results 
•from a change that caused deposition to cease for a considerable 
span of time, and it normally implies uplift and erosion with loss 
of the previously formed record. An unconformity is of longer 
duration than a diastem. (2) The structural relationship between 
rock strata in contact, characterized by a lack of continuity in 
deposition, and corresponding to a period of nondeposition, weath- 
ering, or esp. erosion (either subaerial or subaqueous) prior to 
the deposition of the younger beds, and often (but not always) 

238 



marked by absence of parallelism between the strata; strictly, the 
relationship where the younger overlying stratum does not "conform" 
to the dip and strike of the older underlying rocks, as shown 
specif, by an angular unconformity. 

unconsolidated material: (1) A sediment that is loosely arranged or 
unstratified, or whose particles are not cemented together, occur- 
ring either at the surface or at depth. (2) Soil material that is 
in a loosely aggregated form. 

visible radiation: EMR of the wavelength interval to which the human 
eye is sensitive, theoSpectral interval from approximately 0.4 to 
0.7 ym (4000 to 7000 A). 

volcanic rocks: A generally finely crystalline or glassy igneous rock 
resulting from volcanic action at or near the Earth's surface, 
either ejected explosively or extruded as lava. The term includes 
near-surface intrusions that form a part of the volcanic structure. 

wavelength (symbol x) : Wavelength = velocity/frequency. In general, 
the mean distance between maximums (or minimums) of a roughly 
periodic pattern. Specifically, the least distance between par- 
ticles moving in the same phase of oscillation in a wave distur- 
bance. Optical and IR wavelengths are measured in nanometers 
(10"9m), micrometers (lO-^m) and Angstroms (10~^0m). 

weathering: The destructive process or group of processes constituting 
that part of erosion whereby earth and rocky materials on exposure 
to atmospheric agents at or near the Earth's surface are changed in 
character (color, texture, composition, firmness, or form), with 
little or no transport of the loosened or altered material; specif, 
the physical disintegration and chemical deposition of rock that 
produce an in-situ mantle of waste and prepare sediments for trans- 
portation. Most weathering occurs at the surface, but it may take 
place at considerable depths, as in well-jointed rocks that permit 
easy penetration of atmospheric oxygen and circulating surface 
waters. Some authors restrict weathering to the destructive pro- 
cesses of surface waters occurring below 100°C and 1 kb; others 
broaden the term to include biologic changes and the corrosive 
action of wind, water, and ice. 

window: A band of the electromagnetic spectrum which offers maximum 
transmission and minimal attenuation through a particular medium 
with the use of a specific sensor. 



239 



APPENDIX C 
BASIC IMAGERY INTERPRETATION 

1.0 INTRODUCTION 

The application of remote sensor data to geological analysis, 
i.e., photointerpretation, has been conducted commercially for 50 
years. It was, however, only after World War II, when a large number 
of geologists trained by the military services in photo-intelligence 
were released from service that the use of photogeology became wide- 
spread. The trafficability and engineering aspects of photointerpre- 
tation were largely ignored as the applications were primarily for 
petroleum and mineral exploration. 

The use of remote sensor data is similar to many other survey 
techniques in that the attainment of optimum results requires training 
and continued practice of the skills. A competent geologist is not 
necessarily a competent image analyst and interpreter. Too often 
image interpretations are made by an individual (s) not adequately 
qualified!/ to extract full information from the imagery. The quality 
of the analysis for the particular project suffers as does the project 
manager's inclination to use that particular approach on another 
project. The proficient use of imagery from sensors other than con- 
ventional aerial cameras requires further skills which most geologists 
do not have the opportunity to adequately develop. Although there are 
reams of literature discussing various aspects of imagery interpre- 
tation both photographic and non-photographic, the very mass of data 
discourages use. Some of the better references for interpretation 
guidance are the manuals published by the American Society of Photo- 
grammetry, particularly the two-volume compilation on remote sensing 
just published (Am. Soc. Photogrammetry, 1975). The following brief 
discussions, however, are an attempt to present salient points which 
will aid the geologist and engineer in the interpretation of remote 
sensor data. 



1/ 



This factor is difficult to assess as the individual himself is 
not necessarily qualified to judge his competence. After three 
months of rather concentrated imagery analysis, the individual 
will no doubt feel that he is well-qualified. Experience of 
companies specializing in photogeological services has shown that 
on an average a year of continued daily application of photo- 
interpretation skills is required to attain full proficiency in 
photoanalysis. This is assuming a geologist of B.S. level with 
course work in structure and stratigraphy. 

240 



Black-and-white aerial photography is the most widely used pro- 
duct from remote sensors, and, without doubt, the most highly developed. 
Consequently, this discussion will devote considerable space to the 
use of this medium. Much of the data presented can be applied to the 
analysis of other imagery as well. 

Color and color-infrared photography have been improved substan- 
tially over the years but still lack the resolution of black-and-white 
panchromatic film. They add another dimension to the analysis and 
should be used when possible in conjunction with or in place of black- 
and-white photography. 

In tunnel siting studies the stereoscopic interpretation of 
medium-to-large-scale aerial photography is usually a part of the 
initial data-gathering source for preliminary lithologic and struc- 
tural interpretation. Although existing photography is normally used 
in this phase, it is not necessarily the best choice. The conditions 
that existed at the time of image acquisition can drastically in- 
fluence the interpretability and information content of the image. 
Normally, in temperate zones the best time for image acquisition for 
geological analysis is in late fall or early spring when vegetational 
differences are the most contrasting. In areas where vegetational 
cover is extensive, as in the eastern half of the United States, 
photography should be acquired when leaf cover is minimal. 

Patterns visible from aerial photographs usually provide adequate 
data for lithologic reconnaissance, particularly in areas where bed- 
rock is exposed. However, experienced photointerpreters may be able 
to identify lithologic units even where bedrock may be obscured by 
soil or vegetative cover. By noting the topography, rock and soil 
color, vegetative zoning, primary and secondary structure, and solu- 
tion topography on the aerial photography, an accurate identification 
of lithology is usually possible. Stratigraphic irregularities, and 
therefore faulting, are normally more evident on aerial photography 
than in the field. The photography will certainly identify areas that 
need additional checking in the field. 

The presence of certain potentially hazardous lithologies in a 
test area should be carefully investigated. For example, limestone in 
a temperate-to-humid climate may contain cavernous, structurally weak 
zones, which could initiate collapse of a tunnel. Collapse in lime- 
stone strata is more probable where the rock contains groundwater in 
fractures which chemically weathers the limestone. Structural failure 
may occur in sequences of permeable- impermeable lithologies where 
groundwater seepage may lubricate the zone and initiate slippage. 
Certain sedimentary sequences are incompetent, and should be avoided 
where possible, and experienced photogeologists also consider the 
variation in rock competency as it may be influenced by climatic 
regions. 



241 



Photogeology is a powerful tool for structural geology. The 
attitudes of rock (strike and approximate dip) are normally apparent 
on aerial photographs. Fault and fracture zones are equally apparent, 
largely because of the effects of long-time differential weathering 
and erosion, or by stratigraphic disruptions which are indicative of 
faulting. 

The initial identification of linears on small-scale (1:80,000- 
1:120,000) aerial photographs is important in the site selection 
phase, especially if the lineations represent fracture or fault zones 
which could contribute to lithologic weakness and water leakage within 
the tunnel. These zones should be further investigated and where 
significant, eliminated as potential tunnel locations. (Larger scale, 
i.e. <1:20,000) photography can be utilized by photogeologists to 
obtain more detailed geologic information in the more desirable 
locations. With this approach field work is reduced, as well as the 
total expense of the project. 



242 



2.0 PHOTOGEOLOGICAL INTERPRETATION KEYS 

The systematic application of five important "keys," developed by 
Professor Donald J. Belcher of Cornell University, will lead to the 
identification of a landform. These "keys" are topography, drainage, 
erosion, vegetation, and image tone. Using overlapping photographs and 
a stereoscope, ewery landform is identified by its own specific varia- 
tion of the five keys. 

Instrumental to the analysis of a landform is its topographic 
expression which is easily determined from the photographs using ster- 
eoscopic vision. A topography noted to rise sharply and steeply nor- 
mally represents a terrain which is shallow to bedrock, whereas a yery 
flat topography may represent an extremely deep mantle of residual soil, 
with bedrock existing at depth. In the stereoscopic analysis of aerial 
photographs, topography is the most prominent and obvious feature, and 
is the first key to be applied. 

The second key, drainage , is one of the more important characters 
of a landform, and the drainage interpretation quickly eliminates im- 
probable landform. The drainage pattern consists of the headwaters, 
tributaries, and the major stream and the pattern must have originated 
on the landform. Surface drainage reflects the character of the land- 
form, the most important of which is its permeability. In comparing two 
landforms, the one with the greater number of drainage channels per unit 
area is often the less permeable. A controlled drainage pattern ex- 
hibiting tributaries that are straight or angular may indicate a shal- 
low-to-bedrock landform which contains joints or fractures. In such 
areas excavation could be difficult and expensive. However, in hydro- 
geological investigations, the presence of these angular tributary 
channels, in an otherwise impermeable water-tight landform, may indicate 
fractured or faulted areas containing groundwater. 

It is important to note on the photographs any change in surface 
drainage patterns, as this may indicate a complete change in landform. 
The major types of drainage patterns are dendritic, pinnate, rectangu- 
lar, trellis, parallel, radial, and internal. 

A dendritic drainage system exhibits a "tree-like" drainage pattern 
(Figure 49A), consisting of an integrated tributary system. Two impor- 
tant categories of landforms containing a dendritic pattern are imperme- 
able, unconsolidated deposits and horizontally bedded sediments con- 
sisting of easily weathered bedrock. 

A rectangular drainage system is actually a dendritic pattern which 
is strongly controlled by resistant bedrock (Figure 49B). In this case, 
the tributary channels are sharply angular or straight which is indi- 
cative of shallow-to-bedrock areas. 



243 





A. DENDRITIC 



B. RECTANGULAR 





C. TRELLIS 



D. PARALLEL 



Figure 49A - A-D. Some of the basic drainage patterns which provide information as to the lithoiogy and structure of an area. 



244 



A trellis drainage system (Figure 49C) is generally indicative of 
tilted sedimentary rocks of diverse lithologies. The drainage pattern 
is a manifestation of non-uniformity within the landform, representing 
non-uniform weathering among these lithologies. 

A parallel drainage system is best seen on photomosaics or on 
small-scale photographs where drainage flow is toward the direction of 
regional slope (Figure 49D). 

A radial drainage system (Figure 49E) also is best observed on 
wide-area photographic coverage. It develops in areas with regional 
highs or lows where the channels originate either from the high or 
terminate at the low. Intrusive bodies can be delineated where the 
drainage pattern changes abruptly to a radial system. 

Sedimentary strata that have been warped into domal or anticlinal 
and synclinal folds develop an angular drainage pattern (Figure 49F) 
between the more resistant strata and reflect the character of the 
structure. This drainage pattern is normally accompanied by a radial 
pattern in the center of the structure. 

A pinnate "feather-like" drainage pattern is also a modification 

of the pure dendritic form (Figure 49G). This pattern is an almost 

sure indication of silt-size, unconsolidated deposits, such as loess, 
mica schist derived soil, or volcanic ash. 

An internal drainage pattern (Figure 49H) is indicative of highly 
permeable landforms where the development of surface drainage is all 
but impossible and groundwater flow becomes the norm. The probability 
of seepage problems during excavation is high in these landforms. 

The third key, erosion , is the most important direct clue used in 
the aerial photographic identification of soil texture. Erosion, in 
the form of gully erosion, occurs in landforms where water initially 
collects as surface runoff and creates definite scars of soil removal. 
Gullies occur only in the soil mantle, terminating where bedrock is 
encountered; therefore, gullies are only a clue to bedrock identifica- 
tion where the weathered soil profile is a reflection of the primary 
parent rock type. The characteristics of a gully are unique to speci- 
fic cohesive or non-cohesive soil textures. Gully analysis is the 
most difficult of the five keys to master, but it can be a powerful 
tool in any landform interpretation. 

Vegetation , the fourth of the "keys" to be discussed, can be of 
interpretative value in a general sense, but if the interpreter has a 
strong background in the plant sciences, it can be an even more useful 
tool. There can be no set rules for vegetation analysis as applied to 
landforms as it is a complex system with incredible diversity and 
variation per climatic regime. 



245 





E. RADIAL 



F. ANNULAR 




f "* /? 



o 
Or 















G. PINNATE 



H. INTERNAL 



fj 



Figure 49B - E-H. Some of the basic drainage patterns which provide information as to the lithology and structure of an area. 



246 



In most temperate regions, a greater concentration or larger 
physical dimension of the vegetation reflects increased moisture 
availability of the soils in that region, and if this occurs in a 
pronounced linear zone, it could reflect the existence of a water 
carrying fault zone. 

In areas of flat-lying sedimentary rocks, vegetation often is 
specific to a certain marker bed; in temperate regions, it is common 
to note on the photographs a distinctive "contour-like" map of denser 
bands of vegetation following shale rather than sandstone outcrops. 
Here, the shale slopes are usually less steep and the derived soil 
cover more fertile and moist than that of the sandstone slope. (This 
trend may be reversed in more arid climates where the sandstone beds 
may contain more water, and thus support more vegetation). 

Tone , which refers to the lightness or darkness of the photo 
image, is the last key to be discussed because it is the least reli- 
able and accurate. However, tone can be an invaluable criterion when 
combined with the four previous keys and used by an interpreter exper- 
ienced in soils, geology, and the analysis of aerial photographs. 

On black-and-white photographs, a dark photographic tone is 
generally associated with a terrain of a high soil moisture content 
or soils with a high clay and organic fraction, which, in turn, sup- 
ports a dense vegetative cover. Moreover, the presence of a high 
moisture content reduces the reflectivity of a soil and produces a 
dark photographic tone, even when not marked by a vegetative cover. 
However, in areas of excessive moisture such as a swamp, the photo- 
graphic tone may be very light (close to white) due to a cover of 
light green swamp grass. In general, a light photographic tone is 
associated with permeable, coarse textured soils. 

Varied tones in a cultivated field, visible on black-and-white 
aerial photographs as light streaks or blotchy areas in bare soil or 
by patches of less vigorous cropland, may be indicative of shallow 
bedrock areas. Dark toned streaks in cultivated fields, noted con- 
tinuously during the growing season, may indicate joints in the under- 
lying bedrock. Here, a patchy crop may be evident because of too wet 
conditions created by the moist, weathered, rock zone in the joint. 



247 



3.0 LANDFORM ANALYSIS 

This chapter is a general summary of the methodology used by 
aerial photointerpreters for the analysis of some of the more common 
sedimentary, igneous, and metamorphic landforms. 

3.1 Sedimentary Landforms 

3.1.1 Clay Shale 

Clay shale consists of thinly bedded indurated clays, 
which are highly impermeable and easily eroded. In humid 
climates, the landform is a gently rounded landscape with a 
vertical relief of up to approximtely 400 meters. In more 
arid or semi -arid areas, the topography is more rough and 
the hills exhibit nearly vertical sideslopes. Due to the 
inherent weakness of the landform, a dendritic drainage 
pattern is normal . 

The derived soils contain a significant argil lie 
fraction, creating a fair regime for agriculture. Contour 
plowing is not necessarily practiced on the slopes as the 
soil is not highly erodible; however, clay gullies usually 
are active somewhere on the landscape. (Clay shales may be 
confused with unconsolidated upper coastal plains, but the 
coastal plains because of their erodability, are usually 
contour plowed and this is evident on the aerial photo- 
graphs.) 

Landslides are a common phenomenon, especially if the 
clay shale is overlain with a pervious cover allowing water 
to accumulate at the pervious-impervious contact. 

3.1.2 Sandy Shale 

Sandy shale consists of thinly bedded sandstones (or 
sediments containing a significant sand fraction) inter- 
bedded with thin clay shale seams. Topographically, the 
landform often reaches 2500 meters; a massive, slightly 
rounded topography results because of the weathering and 
eroding off of the sandstone followed by the rounding off of 
the clay shale seams. The landform is fairly impermeable 
because of the plugging effect of the clay seams, and sur- 
face run-off creates a dendritic drainage pattern. 

If the layering within the sandy shale landform con- 
sists of fairly thin beds, smoothly rounded slopes result; 
however, where more massive beds of sandstones-clay shales 
occur, steep sided sandstone outcrops maintain contact with 
the more gently sloping clay shale outcrops. This phen- 
omenon is caused by differential weathering between the 

248 



lithologies. This ragged, rough side slope may be marked 
with landslides at contacts of the more permeable sandstones 
and the underlying shales. Because of the differential 
weathering characteristics of these members, derived soil 
specific to the parent lithology results, often with a 
specific vegetative cover. On the photographs, a distinct 
"contour-like" map of the differing tones of these various 
derived soils and surface vegetation can be traced as marker 
beds. 

3.1 .3 Sandstone 

The pure sandstone landform is massive, permeable, 
and resistant to erosion. In humid climates the topography 
is rolling to bold hills, but in the more arid areas the 
erosion of joints creates steep, vertical cliffs. The 
permeability does not permit surface runoff, and drainage 
occurs only in the well -developed system of joints, creating 
a regional rectangular drainage pattern. 

The derived soil is usually shallow, as the slopes 
are too steep for extensive soil profile development and 
they are droughty and rather infertile; therefore, in most 
regions the vegetation is usually left in the virgin state. 
In the tropics, a deep soil cover can easily exist because 
of the excessive chemical weathering common to these cli- 
matic regimes. Where not mantled by low reflecting vege- 
tation, the photo tone is light. 

3.1.4 Limestone 

In humid regions, limestone is valley-forming and 
topographically low, but in the more arid regions it is 
among the most resistant of the highlands. Limestone is 
extremely susceptible to chemical weathering, and because of 
the virtual lack of this process in dry regions, it exists 
as massive and durable highs. The limestone - lowland 
boundary is sudden and sharp because limestone possesses an 
internal drainage system which is incapable of depositing 
alluvial fans at the boundary. 

In humid regions, the collapse of many sinkholes 
along joints in the rock that concentrate groundwater flow, 
creates linear, steep sided, flat bottomed valleys, usually 
devoid of tributaries. 

The drainage pattern is internal, consisting of sink- 
holes perhaps with "lost" rivers. These rivers may dis- 
appear into a sinkhole and then reappear at a distant locale. 
If a drainage pattern is noted on the photos adjacent to an 

249 



internally drained limestone area, another landform, perhaps 
a shale, has been encountered. 

The trend of soils developed from limestone is to 
have a significant silt content. The soil gullies in these 
limestone derived soils are light to white toned, and they 
have collapsing cup-like gully heads. Where sinkholes are 
bordered by white radial lines, it is inferred that they are 
actively collapsing, the light lines being unvegeta ted soil 
scars. Often, white toned "blotches" are noted where water 
seeps out from outcrops and precipitates calcium carbonate. 

If landslides are detected on the photography, ano- 
ther more impermeable landform is present under the lime- 
stone, as landslides are not characteristic of pure thick 
limestone. 

3.1.5 Tilted Sedimentary Rocks 

A few statements concerning tilted sedimentary rocks 
are warranted. Unless the landform is a tilted pure clay 
shale, a trellis drainage pattern will be present. Where 
clay shale is a member, it often forms the valleys, as it is 
so easily eroded, and its local drainage pattern is den- 
dritic within the total trellis system. In humid regions 
limestones also form valleys, leaving the sandstones as the 
adjacent highlands. Tilted limestone often has oblong 
sinkholes, reflecting the sloping groundwater table. Also, 
a definite linear boundary occurs between an intrusion and 
tilted sedimentary rocks. 

3.2 Igneous Landforms 

3.2.1 Granite 

Granite, an intrusive of felsic composition, produces 
three distinct topographies. In the tropics, massive dome 
shaped hills of varying elevations created by an exfoliation 
process are common. In precambrian shields, the rock main- 
tains a fairly low topographic expression normally charac- 
terized by thousands of lakes. In higher altitudes or in 
climatic regions where physical weathering is of more sig- 
nificance than chemical weathering, "A-shaped," massive 
mountains are common. In all three cases, stress relief 
fractures abound and are easily identified on the aerial 
photographs. These fractures seem not to have a definite 
orientation, unlike those of sedimentary landforms. 

The boundary between granite and bodies of water is 
irregular, reflecting the difficulty of smoothing-off the 
granite shores. With careful stereoscopic interpretation, 

250 



it is common to be able to identify large granitic boulders 
which have fallen into the water, or which mantle the sur- 
face of the intrusion. 

Alluvial fans issuing from this landform are often 
granular, steep sided, and of significant size. Springs 
issuing from their edges may contain dense patches of vege- 
tation as evidenced by darker photographic tones. 

The drainage pattern is regionally dendritic, however, 
local "pincer-like" drainage is locally superimposed, indi- 
cating that the drainage must curve locally around resistant 
granitic masses. 

The soils derived from granite vary depending upon 
the climatic regime and upon the chemical composition of the 
granite. In general, granitic derived soils in the tropics 
become sandy clays, those in the artic are granular, and 
those in temperate climates fall somewhere in between, 
depending on parent rock composition. Only a careful stereo- 
scopic analysis of the gully development will determine the 
soil type. 

The tone of granite is generally light, except where 
fractured or faulted. Here, the deeper weathered soil zones 
contain more moisture and a linear, darker photographic tone 
results. The intersection of these fractures or faults are 
potential aquifers sought for in groundwater exploration, 
but they may be zones of seepage in tunnel excavation. 

3.2.2 Basalts and Fast Cooled Lavas 

Basalt flows maintain an irregular, almost pitted 
surface due to collapse of the rock during the cooling 
process and also to subsequent collapse following internal 
stream erosion. These depressions may become filled with 
windblown debris, creating a pock-marked, "lizard-skin" 
appearance on the aerial photography. Recent lava flows 
terminate in a lobate form, unless encountering a water 
body, and their surface is "wrinkled" due to cooling irreg- 
ularities within the lava body. 

Basalt is extremely permeable due to the formation, 
during cooling, of columnar joints. Precipitation per- 
colates into these joints and a lack of surface drainage 
results. Because the extrusives usually flowed down existing 
valleys before cooling, many flows now mantle pre-existing 
buried watercourses. The internal drainage of the permeable 
basalt or lava may concentrate into these watercourses, 
forming great aquifers for groundwater. 

251 



Regionally, a parallel drainage pattern is present. 
A local surface drainage pattern results from impermeability 
caused by inter-layers of basalts or lavas and their derived 
cohesive soils. Landslides are common in basalts overlying 
more impermeable stratum, for water seepage lubricates the 
zone of contact, causing the slides. Potential landslide 
areas can often be delineated by noting darker toned zones 
of water accumulation on the surface of a scarp. 

Basalt talus, present at the bottom of scarps, is a 
noteworthy photointerpretation clue. The bounding scarps 
maintain a jagged, saw-toothed appearance due to the col- 
lapse of the columnar jointed columns. Also, horizontal 
stratification lines are usually obvious on cliff faces. 

3.2.3 Tuff (volcanic ash deposit) 

A steep topography, a fine-textured, dendritic drain- 
age pattern, pronounced silt gullies, and excessive erosion 
characterize the landform produced on volcanic ash deposits. 
In general, the hills are knife-edged, and over broad areas 
the elevation of the hilltops do not conform to any given 
elevation, but rapidly decline toward the lowland boundary. 
Because of the erosiveness of the tuff, the lowland boundary 
has numerous indentations. The steep highlands have equal 
sideslopes, indicating deep and uniform materials. 

3.2.4 Interbedded Pyroclastics and Flows 

Interbedded pyroclastics and flows have a gentle and 
subdued boundary with the lowlands. When a flow surface has 
not been highly dissected, the original flow pattern is pre- 
served, but with moderate dissection, it generally forms 
sloping ridges with roughly parallel branches. The surface 
drainage is moderately developed and generally integrated 
into a dendritic pattern, with roughly parallel, often 
sickle-like, branches. 

Most extrusives, regardless of composition, can be 
identified by their ragged and rough outcrops. Unlike 
sedimentary rocks, where marker beds can usually be traced, 
volcanics tend to crop out in an irregular pattern, re- 
flecting the probable irregular pre-flow topography which it 
mantles. 

3.2.5 Dikes 



Dikes, when their compositional material is more 
resistant to erosion than the surrounding rock mass, form 
topographic highs. Groundwater may be dammed at depth when 
encountering these impermeable landforms. 

252 



3.3 Metamorphic Landforms 

3.3.1 Gneiss 

Mollard (1957) describes gneiss topography as follows: 

1) At the contact with water bodies, gneiss maintains 
a highly irregular shoreline. 

2) In shield areas, gneiss is foliated, showing a 
characteristic wavy banding. There are truncated 
folds composed of metamorphosed sedimentary rocks 
(metasediments) and local "scraps" of contorted 
metasediments that occur on the largely granitic 
shield. 

3) In temperate areas, the gneiss forms anomalous 
large ridges which are locally sinuous and sub- 
parallel in plan view. 

4) In sub-tropical areas, gneiss occurs as softly 
rounded, smooth, low hills with non-accordant 
ridge summits. No banding or foliation is appar- 
ent. 

The drainage pattern is rectangular dendritic, for 
the drainageways intersect at nearly right angles and the 
tributaries have abrupt bends, forced by fracturing and 
foliation of the bedrock. Regionally, the dendritic drain- 
age pattern may be somewhat parallel because of a ridge and 
valley topography. 

The derived soils are extremely erosive, and contour 
plowing is practiced on the slopes. 

3.3.2 Schist 

Schist in hand samples is thinly laminated. Aer- 
ially, schist terrain is also banded, on a much larger 
scale, and the difference in resistance to weathering within 
these bands creates a somewhat parallel topography. A more 
rough topography exists in arid than in more humid climates 
and the parallelism of the uplands in arid regions is pro- 
nounced. However, in humid climates a deeply weathered zone 
may mantle and subdue the topography. Here, the schist is 
well dissected, producing hills with rounded crests and 
steep sideslopes. In all climates, the drainage pattern is 
rectangular. 



253 



The soils vary from a sandy silt to a sandy clay, 
depending upon climate and parent rock mineralogy. The 
gullies are closely spaced, long, and parallel in humid 
regions (Mollard, 1957). 

3.3.3 Slate 

Topography produced on slate is rugged in both humid 
and arid areas, the size of the hills being fairly uniform 
and small. The drainage pattern is fine textured, rectangular 
dendritic, and the gullies are steep and parallel, entering 
the tributaries at nearly right angles. The residual soil 
is relatively infertile and vegetation usually remains in 
the virgin state. 

3.3.4 Serpentine 

Serpentine masses form long sinuous ridges having 
smooth surfaces and convex sides. Such ridges connect 
elongated cone-shaped hills which become more and more 
rounded and independent from the main mass as dissection 
progresses. When bounded by water, the shoreline is smoothly 
curving with numerous indentations. Only regionally is a 
dendritic drainage pattern developed. The gullies are short 
and steep, the soil normally weathering to a clay, but 
varying from a silty clay to bare rock. 

A significant photointerpretation clue is that soils 
developed from serpentine are highly infertile, and no 
matter the climatic regime, they support a lesser concen- 
tration of vegetation than adjacent areas. This is often 
the first clue to the presence of a serpentine body. 






254 



APPENDIX D 
LOW SUN ANGLE PHOTOGRAPHY (LSAP) MISSION PLANNING 

1.0 DISCUSSION 

Low sun angle photography can be acquired with either conven- 
tional panchromatic aerial film or with black-and-white infrared film 
and a red filter. The image contrast for LSAP should be greater than 
for normal black-and-white aerial photography. Thus, if panchromatic 
film is used, it should be processed in a high contrast developer and 
printed on high contrast paper. Some experimentation may be needed to 
attain the desired results. 

Timing of the overflight for a specific solar elevation is cri- 
tical and this should be emphasized to the pilot and photographer. In 
order to document the overflight parameters the camera should be 
equipped with a data chamber that includes an operating clock that can 
be read to the nearest minute. The data chamber should also include 
the altitude and correct date. The appropriate "standard time" to be 
used should be clearly specified. 

The photographic crew will need a schedule of flight times for 
several dates in the event that weather or other factors preclude 
overflights on a specific day. 

The selection of solar elevation and azimuth for optimum enhance- 
ment of geology is dependent upon the relief in an area and the slope 
of topographic features. LSAP is most effective in areas of low (5- 
10'; 1.5-3 m) to moderately high local relief (2000' -4,000' ; 610- 
1220 m). To cast the shadow, the angular elevation of the sun above 
the horizon must be less than the ground slope angle. The percent 
shadow needed for the best enhancement of topographic features is 
subjectively judged to be between 25% and 50% of the image area. 
Topographic maps of the target area should be closely examined to 
determine the best solar elevation and azimuth for shadow enhancement 
of terrain features. The azimuth of the sun depends upon the season, 
and at different times of the year, shadows will fall in a range of 
directions. Care must be taken to plan LSAP missions so that shadows 
will not obscure important topographic features. Figure 50 is a 
hypothetical topographic situation which illustrates the importance of 
selecting the proper azimuth for shadow enhancement of geologic fea- 
tures at low solar elevation at certain times of the year. 

Suppose the geologic features in the valley (Figure 50) need to 
be investigated using the shadow enhancing technique. If a solar 
elevation of 15°, azimuth 70° is used the ridge will be shadow en- 
hanced but the sink hole and any other geologic features in the valley 
will be obscured by shadow. If an angle of 25°, azimuth 70° is used 
the ridge will still be enhanced but the sink hole still will not be 

255 



140° RIGHT AZIMUTH 
DECEMBER 22 
B 



70° RIGHT AZIMUTH 
JUNE 22 




E 90° 



SUN 



SUN 



SHADOW tNHANCEMENT OF TERRAIN ON JUNE 22 a» 



4000 

o s 

5 2 3900 

> -S 

III re 

uj S 



,t 




SUN 



B 



SHADOW ENHANCEMENT OF TERRAIN ON DECEMBER 22 



B' 



Figure 50 - An illustration of the importance of selecting the proper azimuth to enhance geologic features (for complete 
discussion see text). 



256 



detected. If, however, a solar elevation of 15° is used with an 
azimuth of greater than 128° then shadow enhancement of the sink hole 
will occur. 

The angular elevation of the sun changes at a maximum rate of 1° 
ewery four minutes (15° per hour). The overflight time of LSAP mis- 
sions, therefore, must be precise in order to obtain the desired 
shadow enhancement of topographic features. One can determine when to 
make LSAP overflights by: 

1. Mathematical calculation of the desired solar elevation and 
azimuth. 

2. Graphical solution using time and azimuth charts in the 
Smithsonian Institution Meteorological Tables. 

3. Actual on-site observations of the shadows. 



2.0 MATHEMATICAL CALCULATION OF SOLAR ELEVATION AND AZIMUTH 

The solar elevation and azimuth can be calculated using the 
following formulas: 

SINa = SINcf) SINa + COS(}) COSa COSh (1) 

The formula for the calculation of solar azimuth is: 

- COSa SINh 

SINcc = (2) 

COSa 

a = elevation of the sun (angular elevation above the horizon) 

(j) = latitude of the observer 

a = declination of the sun 

h = hour angle of the sun (angular distance from the meridian 
of the observer) 

SINa - SINcj) SINa 

COSh = (3) 

COS(j) COSa 

Formula 3 can be used to calculate the precise time to make an over- 
flight to obtain a desired solar elevation. 



257 



The declination of the sun can be obtained from Table 12. The 
latitude of the observer should be expressed in degrees and fraction 
of degrees. The hour angle is the time of day expressed as an angle 
formed by the intersection of a line drawn from the sun to the center 
of the earth and a line drawn from the solar zenith to the center of 
the earth. The hour angle is graphically represented in Figure 51. 




\ 



\ 



Figure 51. Graphic illustration of hour angle. 



Z = Solar zenith (12 noon true solar time) at 
point of observation. 

a = elevation of the sun (angular elevation above the horizon). 

h = hour angle of the sun. 

To calculate the hour angle it is necessary to convert the time 
to hours and fractions of hours. Morning times are subtracted from 12 
noon (12 represents the solar zenith at the meridian of the observer). 
The result, in hours and fractions, is then multiplied by 15° to 
obtain the hour angle. For times after 12 o'clock noon, simple multi- 
plication by 15° will yield the hour angle. 



258 



Table 12. EphemeriS of the Sun (primed with permission of the Smithsonian institution) 

All data are for 0' Greenwich Civil Time in the year 19S0. Variations of these data from 
year to year are negligible for most meteorological purposes, the largest variation occurs 
through the 4-year leap-year cycle. The year 1950 was selected to represent a mean condition 
in this cycle. 

The declination of the sun is its angular distance north (-|-) or south ( — ) of the celestial 
equator. 

The longitude of the sun is the angular distance of the meridian of sun from the vernal 
equinox (mean equinox of 1950.0) measured eastward along the ecliptic. 

The equation of time (apparent — mean) is the correction to be applied to mean solar time 
in order to obtain apparent (true) solar time. 

The radius vector of the earth is the distance from the center of the earth to the center of 
the sun expressed in terms of the length of the semimajor axis of the earth's orbit. 



' U. S. Naval Observatory, The American ephemeris and nautical almanac for the year 1950, Washington, 



EPHEMERIS OF THE SUN 





Decli- 


Lon 


gi- 


Equa 


tion 


Radius 


Date 


nation 


tuc 


e 


o( t 


me 


vector 


Jan. 1 


-23 


4 


280 


1 


m. 

- 3 


6. 

14 


0.98324 


5 


22 


42 


284 


5 


5 


6 


.98324 


9 


22 


13 


288 


10 


6 


50 


.98333 


13 


21 


37 


292 


14 


8 


27 


.98352 


17 


20 


54 


296 


19 


9 


54 


.98378 


21 


20 


5 


300 


23 


11 


10 


.98410 


25 


19 


9 


304 


27 


12 


14 


.98448 


29 


18 


8 


308 


31 


13 


5 


.98493 


Mar. 1 


- 7 


53 


339 


51 


-12 


38 


0.99084 


5 


6 


21 


343 


51 


11 


48 


.99182 


9 


4 


48 


347 


51 


10 


51 


.99287 


13 


3 


14 


351 


51 


9 


49 


.99396 


17 


1 


39 


355 


50 


8 


42 


.99508 


21 


- 


5 


359 


49 


7 


32 


.99619 


25 


+ 1 


30 


3 


47 


6 


20 


.99731 


29 


3 


4 


7 


44 


5 


7 


.99843 


May 1 


+ 14 


50 


40 


4 


+ 2 


50 


1.00759 


5 


16 


2 


43 


56 


3 


17 


1.00859 


9 


17 


9 


47 


48 


3 


35 


1.00957 


13 


18 


11 


51 


40 


3 


44 


1.01051 


17 


19 


9 


55 


32 


3 


44 


1.01138 


21 


20 


2 


59 


23 


3 


34 


1.01218 


25 


20 


49 


63 


14 


3 


16 


1.01291 


29 


21 


30 


67 


4 


2 


51 


1.01358 


July 1 


-f23 


10 


98 


36 


- 3 


31 


1.01667 


5 


22 


52 


102 


24 


4 


16 


1.01671 


9 


22 


28 


106 


13 


4 


56 


1.01669 


13 


21 


57 


110 


2 


5 


30 


1.01659 


17 


21 


21 


113 


51 


5 


57 


1.01639 


21 


20 


38 


117 


40 


6 


15 


1.01610 


25 


19 


SO 


121 


29 


6 


24 


1.01573 


29 


18 


57 


125 


19 


6 


23 


1.01530 


Sept. 1 


-f 8 


35 


157 


59 


- 


15 


1.00917 


5 


7 


7 


161 


52 


+ 1 


2 


1.00822 


9 


5 


37 


165 


45 


2 


22 


1.00723 


13 


4 


6 


169 


38 


3 


45 


1.00619 


17 


2 


34 


173 


32 


5 


10 


I.OOSIO 


21 


+ 1 


1 


177 


26 


6 


35 


1.00397 


25 


- 


32 


181 


21 


8 





1.00283 


29 


2 


6 


185 


16 


9 


22 


1.00170 


Nov. 1 


-14 


11 


217 


59 


-fl6 


21 


0.99249 


5 


15 


27 


222 





16 


23 


.99150 


9 


16 


38 


226 


I 


16 


12 


.99054 


13 


17 


45 


230 


2 


15 


47 


.98960 


17 


18 


48 


234 


4 


15 


10 


.98869 


21 


19 


45 


238 


6 


14 


18 


.98784 


25 


20 


36 


242 


8 


13 


15 


.98706 



Date Dccli- Longi- Equation Radius 

nation tudc of time vector 



Feb. 1 -17 19 311 34 -13 34 0.98533 



Apr. 



June 



Dec. 



21 21 246 11 11 59 .98636 



5 


16 


10 


315 


37 


14 


2 


.98593 


9 


14 


55 


319 


40 


14 


17 


.98662 


13 


13 


37 


323 


43 


14 


20 


.98738 


17 


12 


15 


327 


46 


14 


10 


.98819 


21 


10 


50 


331 


48 


13 


SO 


.98903 


25 


9 


23 


335 


49 


13 


19 


.98991 


1 


+ 4 


14 


10 


42 


- 4 


12 


0.99928 


5 


5 


46 


14 


39 


3 


1 


1.00043 


9 


7 


17 


18 


35 


1 


52 


1.00160 


13 


8 


46 


22 


30 


- 


47 


1.00276 


17 


10 


12 


26 


25 


+ 


13 


1.00390 


21 


11 


35 


30 


20 


1 


6 


l.OOSOO 


25 


12 


56 


34 


14 


1 


53 


1.OO606 


29 


14 


13 


38 


7 


2 


32 


1.00708 


1 


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Oct. 1 - 



259 



3.0 GRAPHIC SOLUTION 

Solar elevation and azimuth can be determined graphically by the 
use of a series of charts published by the Smithsonian Institution 
("Smithsonian Meteorological Tables," Publication Number 4014, pp. 
495-505). Figure 52 is an example of a chart for 40° latitude. The 
following instructions for the use of these charts are reprinted here 
with permission. 



40° N 




Approx. dates 
Tune 22 

May 21, July 24 
May I, Aug. 12 
Apr. 16, Aug. 28 
Anr. 3. Sept. 10 
Mar. 21, Sept. 23 

Mar. 8, Oct. 6 
Kek 23, Oct. 20 
Feb. 9, Nov. 3 
Jan. 21, Nov. 22 
Dec. 22 
Complete data in Table 169. 



200 , 

190 SOUTH 170 

SMITHSONIAN METEOROLOGICAL TABLES 



Figure 52 - This chart permits the graphic determination of solar azimuth and altitude for any time or day of the year for 
40° latitude north or south. The chart is one of a series constructed for different latitudes which were published by the 
Smithsonian Institution in their "Smithsonian Meteorological Tables" Publ. No. 4014; reproduced here with permission. 



260 



This series of charts, one for each five degrees of latitude (except 5'^ , 
15^ , 75^ , and 85° ), gives the altitude and azimuth of the sun as a function 
of the true solar time and the declination of the sun as a function of the 
true solar time. Linear interpolation for intermediate latitudes will give 
results within the accuracy to which the charts can be read. 

On these charts a point corresponding to the projected position of the 
sun is determined from the heavy lines corresponding to declination and 
solar time. 

To find the solar altitude and azimuth: 

1. Select the chart or charts aopropriate to the latitude. 

2. Find the solar declination 6 corresponding to the date in 
question from the Ephemeris (Table 1). 

3. Determine the true solar time as follows: 

a. To the local standard time (zone time) add 4 minutes for 
each degree of longitude the station is east of the standard 
meridian, or subtract 4 minutes for each degree west of the 
standard meridian to get the local mean solar time. 

b. To the local mean solar time add algebraically the equa- 
tion of time obtained from the Ephemeris; the sum is 
the required true solar time. 

4. Read the required altitude and azimuth at the point determined 
by the declination and the true solar time. Interpolate linearly 
between two charts for intermediate latitudes. 

Altitude and azimuth in southern latitudes. — To compute solar altitude 
and azimuth for southern latitudes, change the sign of the solar declination 
and proceed as above. The resulting azimuths will indicate angular distance 
from south (measured eastward) rather than from north. 



261 



4.0 VISUAL OBSERVATION 

Approximations of suitable shadow lengths for structural enhance- 
ment of an area can be made by on-site observations. Observations 
made in the morning and evening a day or two prior to the planned 
photographic mission will provide insight as to the time the shadows 
are of appropriate length to give maximum enhancement of the topo- 
graphy. To determine the correct times for following days when shadows 
will be the same length, consult the weather section of the local 
paper or the Weather Bureau for the daily change in time of sunrise 
and sunset. This factor can be added or subtracted from the observed 
time as appropriate when preparing instructions for the flight crew. 

This method lacks precision and it is recommended that supple- 
mental photography be acquired approximately 20 minutes before and 
after the selected time to assure usable photography. For small, 
specific areas such as a tunnel site, this multiple overflight ap- 
proach is of merit regardless of the method of determining overflight 
times. The additional costs will be small. 



262 



APPENDIX E 



FIELD REFLECTANCE STUDIES AT 
CARLIN CANYON, NEVADA 



1.0 SPECTRORADIOMETRIC FIELD INVESTIGATIONS 

On August 5, 1975 during a field trip to the Carl in Canyon site, 
spectroradiometric measurements were made of the reflectance pro- 
perties of the Diamond Peak conglomerate and the Strathearn limestone. 
The measurements were made at two sites with an ISCO, model SR, 
instrument which permits continuous wavelength scanning between 380 
and 1 ,350nm. The sensing bandwidth of the system is 25nm in the 380- 
750nm range and 50nm in the 750-1 ,350nm range. A fiber optic ex- 
tension head with a diffusing disk was used for the field measure- 
ments. Typical rock exposures were selected for measurement with the 
sensing head positioned approximately 12 inches from the rock surface. 
The weather was excellent and the sky clear of clouds, so solar readings 
were taken as a suite of measurements immediately before or after the 
reflectance measurements of the outcrop. A period of approximately 4- 
5 minutes separated these readings. 

Figure 53 are the relative reflectance curves prepared from these 
measurements. They show that there is, with few exceptions, less than 
3% difference in relative reflectance of the two rock materials on a 
weathered surface. 



263 



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WAVELENGTH (nm) 



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^igure 53 - Relative reflectance measurements made with an ISCD spectroradiometer. The results show only minor 
differences in the relative reflectance of the Diamond Peak conglomerate and the Strathearn limestone. 



264 



2.0 FIELD RADIQMETRY 

On October 23, 1975, Dr. R.J. P. Lyon of Stanford University 
joined the Earth Satellite Corporation field crew at Carl in Canyon to 
make measurements with two Exotech Model 800 radiometers. 

The Exotech unit is a four-band radiometer filtered optically to 
match the LANDSAT satellite system. It is a solid state, battery 
powered unit and easily portable. Two of these instruments are nor- 
mally used at once - one pointing upwards for global irradiance measure- 
ments, and one pointing at the target. Lenses of 1° and 15° fields- 
of-view (FOV) are available with 2tt diffusers for irradiance measure- 
ments. 

The field measurements were conducted after the analysis of 
flight data from the 11 -channel multispectral scanner (MSS) indicated 
relatively poor separability channel -by-channel. Some improvement had 
been noted when the MSS channels were combined to approximate LANDSAT 
channels, and it was desirable to verify this fact in the field. 
Field measurements were planned for October 18, 1975, exactly one year 
after the remote sensing overflight, but logistic problems made this 
impossible. It was possible to mobilize five days later on October 23, 
which unfortunately was a somewhat snowy and cloudy day. 

2.1 Exotech Radiometer Field Data (E-Channels) 

2.1.1 Sky Illuminance Effects 

The measurement technique includes the continual 
monitoring of the incoming irradiance of the sky. This 
serves to check for anomalies, either in the global illumin- 
ation (sun plus sky) or in the equipment. A predictable 
pattern of sky readings should emerge from the data set. 

The Carl in sky data showed two populations; one was 
relatively constant when the sky was clear of any clouds, 
and the other quite variable when clouds were actively 
forming and dissipating near the sun. The restriction of 
measurements to that time when the sun was actually clear of 
clouds was not entirely successful. The proximity to the 
sun of existing clouds, or more probable, variations in the 
atmospheric water-ice-snow content and pre-cloud water vapor 
formation, severely attentuated the incoming radiation. 
This was doubly complicating, as a part of the measurement 
technique is to take long, 1° FOV sitings on steep sloping 
outcrops sufficiently far away for the narrow beam to inte- 
grate statistically a large outcrop area (e.g. at 1,000 feet 
(305m) distance the 1° FOV covers 17 (5m) feet of outcrop). 



265 



Often the illumination at the outcrop was not the 
same as the illumination at the instrument station. As a 
consequence, the corrections to the standards were not 
always the same as the corrections needed for a target. 

2.1.2 Field Data Selection 

Because of these problems only about 50/^ of the data 
were selected for further analysis based upon (a) global 
irradiance values which matched predicted patterns; (b) 
duplicate readings; (c) replicated readings (at a slightly 
later time) which were similar; arid (d) vertically-viewed 
data (using the 15° field-of-view, about three square feet 
in size) when factor "a" was acceptable. 

2.1.3 Field Data Reduction 

The Exotech data (E-set) were processed at the Stan- 
ford University Remote Sensing Laboratory by the computer 
ratioing program (ERTSRATS). This program calculates, 
for the sky : 

a) E-channel irradiance {2-n) in units of watts/cm /ym 
band-pass. 

b) Normalized channel irradiance (normalized to lym 
band-pass to take care of the greater band-pass 
width of channel E-7 (LANDSAT 7) which is 2.5 
times the width of channels E4, E5, and E6 with 
units of watts/cm^/ym band-pass. 

c) CIE color coordinates of sky color temperature 
(this is a measure of illumination quality and is 
used for monitoring). Channels E4, E5, and E7 are 
used so as to include solar infrared radiation, 
therefore, correctly, the factor "c" is a "pseudo" 
CIE value, but comparable to the use of color 
infrared film. 

For the target, we calculated similarly: 

d) E-channel radiance (brightness) in units of watts/ 
cm2/ym in band-pass for the four channels. 

e) Normalized R-channel radiance in units of watts/ 

cm^/ym. 

f) CIE coordinates as in Item C above. 



266 



For the target-sky pair we can now calculate several forms 
of reflectance. 

g) Bi-directional reflectance vf the same FOV lenses 
are used on each unit (A or B) and one unit (B) is 
looking down at a horizontal white reflectance 
standard (BaSO^) commercially known as FIBERFRAX 
(see Watson, R.D., 1971). Irradiance (2tt) is not 
measured. 

h) Directional reflectance if the "standard" unit B 
is equipped with Z-n diff users and is viewing the 
sky at the zenith. 

In both cases, the A and B units must be read at 
closely concurrent times, and particularly so under the poor 
and variable lighting conditions that prevailed at the 
Carl in Canyon site (see Section 2.4 for instrumentation and 
technique description on how this is accomplished). 

Suitable factors can be calculated from mixing both 
types of geometry in the data set collection. Unit A with 
r or 15°F0V lenses views FIBERFRAX standards vertically 
below the lenses, while the B unit with 2it diff user views 
the incoming global irradiance. 

Theoretically, this factor should be 1/it or 0.318. 
In practice, we calculate empirically values from within the 
data set matrix for that day, thereby effecting several 
other small normalizations which are advantageous. 

In addition, we calculate several sets of ratios 
including reflectance ratios , and express them usually in 
the sequence used by R. Vincent (Vincent & Thompson, 1973) 
as ratios Ch 7/6, Ch 7/5, Ch 7/4, Ch 6/5, and Ch 5/4£./; 
thereby being able to effect a comparison with a growing 
body of information from several sets of workers as to how 
the LANDSAT spectral signatures and ratios for various 
terrains are correlating with ground measurements. 

2.2 Exotech Results 

Two tables of detailed groupings of rock outcrop areas 
(Tables 13 and 14) and a summary table (Table 15) have been pre- 
pared from the 50 spectra selected and are considered to be free 
from atmospheric problems. 



These numbers refer to LANDSAT multi spectral scanner data chan- 
nels which spectrally have bandwidths as follows: Ch 4 = .5- 
.6um, Ch 5 = .6-.7ym, Ch 6 = .7-.8ym, and Ch 7 = .8-l.lym. 

267 



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These tables list band-pass reflectance values for each 
group (R4, R5, R6, R7) and the ratios of those reflectances 
arranged in the Vincent sequence as R76, R75, R74, R65, R64, 
R541./. Each value is the mean of that group of N measurements 
multiplied by 100, to give an integer value. The value in paren- 
theses is the coefficient-of-variability (GOV) for that mean or 
the percent variability as found by dividj^ng the standard devia- 
tion for that group by its mean (GOV = a/x). 

2.2.1 Summary 

From Table 15 the following observation can be made. 
The R54 ratio has the highest group mean of 196 for the 
targets most red within the conglomerate facies; the "yellow 
area" near Point a; Figure 32 on the hill north of the river 
has the lowest value and is least red with R54 = 147. 
Vegetation (sagebrush) is intermediate with an R54 value of 
162, similar to the sandbar with R54 of 170. An image of 
R54, therefore, should be a moderate discriminator showing 
about 33% contrast— , with the conglomerate highest or white 
and the yellow area lowest or dark gray. 

The R54 ratio as detailed in Table 15 indicates the 
four localities of conglomerate have a group mean value of 
R54 = 196, but the individual localities show considerable 
variation; North Hill, R54 = 207, and the red patches near 
Carl in Peak summit above the tunnel, R54 = 208. These sites 
have extra contrast of 14% as compared to the spur, R54 = 
183, and on the northeast portion of the river bend R54 = 
185, all sites which have similar facies. Thus, they should 
(and do) show as brighter patches or higher image contrast 
areas on the R54 imagery, even relative to the other out- 
crops to the same conglomerate facies. 

Ratio R74 has a much better group mean spread with 
conglomerate (252), contrasting with the sandbar (186) and 
the yellow area (160); this gives 58% contrast as defined 
above. 

An image of R74, therefore, should show conglomerate 
as light toned, sand intermediate and the yellow area darker 
gray. 



3/ 



This shorthand notation used was originated by R. Vincent (1970) 
for designating ratios by channel number. For example, R64 
indicates a ratio of Channel 6/ Channel 4. 



i/ 

Contrast = max/minimum. 



271 



Sixty-four characteristics similar to R74, but with a 
group mean for conglomerate of 205, the yellow area, 167 and 
the sandbar, 169. This should reverse the image contrast 
making the sequence: conglomerate lightest in tone and the 
yellow area and sandbar medium gray. 

The vegetation (sagebrush) may be discriminated using 
R75 or R65 with the sagebrush brightest with group mean 
values of 159 and 136 for the two ratios, with conglomerate 
showing 128 and 103 equally with limestone, the sandbar 
showing 109 and 99, and the yellow area showing 110 and 117. 

The coefficient-of-variability (GOV) of group means 
in the parenthetic statement in the lowest line of the table 
may be used as a crude measure of the relative discrimin- 
ability of each variable - the larger the GOV the greater 
the spread of the means (provided the populations have 
comparable standard deviations). Thus, R75 with a GOV equal 
to 0.19 would be the best to maximize the data spread. A 
tabulation R75 contrast is as follows: conglomerate 17%; 
limestone 13%; sandbar 0%; indicating a 17% spread in the 
three rock types. 

Both R75 and R65 are vegetation sensitive; thus, R74 
with group mean GOV equal to 0.15 is the best for rock 
discrimination. The R74 lithology contrasts are conglomerate 
35%, limestone 9%, and the sandbar 0%; a spread of 35% 
contrast between the sandbar and the conglomerate. 

2.3 Bar Graph 

A bar graph (Figure 54) has been prepared to show visually 
the spread of group ratio means R54 and R75 (plotted as the 
abscissa). The horizontal extent of the symbol indicates a la 
spread. Where n is equal to or less than three, values which are 
plotted directly as a have no real meaning. 

The ordinate is artificial and represents an attempt to 
portray the size (n) of each group to give some meaning to the 
standard deviation spread. Inspection of the graph indicates 
that an R75 is a good discriminant for limestone, whereas an R54 
is a better discriminant for conglomerate. 

The field measurement data and the flight imagery strips, 
while both showing low contrasts, do substantiate each other 
rather well. This is so regardless of the fact that the field 
data are all for small outcrop areas up to 20 feet or so in 
diameter and the imagery analyst is viewing much larger areas of 
terrain. 



272 



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273 



Ground measurements of the kind detailed above should enable 
one to predict the image contrast on later flight imagery and aid 
in selection of multi spectral scanner bands to be composited for 
better enhancement in the final three-band color presentations. 

2.4 Supplemental Information on Exotech Reflectance Measurements 

The field instrumentation used was two Exotech four-channel 
radiometers which are filtered to match the four LANDSAT satellite 
filters and a Fluke multimeter (Type 8,000) for digital readout 
of the eight channels (four upward-viewing, four downward-target 
viewing). 

The principal advantage of the units are: 

• Very portable, weighing about four pounds for each 
unit. 

• Battery powered (rechargeable). 

• Solid rugged design, using solid state amplifiers 
and silicon detectors. 

The total system, including a standard reflectance panel can 
be easily carried by two men over average terrain. A typical 
measurement profile involves the following: 

1. Mount the Exotech radiometer with the diffusing disks 
on the upward-viewing unit to measure the 2tt irradiance 
of the infalling sunlight. The 15° field-of-view (FOV) 
lenses are usually used for these close-up views. 

2. Mount downward-viewing unit in proximity to the other 
unit to view the reflectance standard (we used FIBERFRAX 
sheets, a refractory fiber sheet which has good photo- 
metric properties and a 90+% reflectance between 400nm 
and 2.5ym). 

3. Attach the swith box and Fluke multimeter to record the 
digital output (the switch box allows one to switch 
rapidly from Channel 4-up to Channel 4-down; to 5-up to 
5-down, etc. All eight channels can be read in about 
30 seconds). Figure 55 is a typical calibration setup. 
Each of the up and down pairs of readings required for 
reflectance ratios are made within ten seconds of each 
other, greatly alleviating the drift effects due to 
rapid changes in the atmospheric transmission - at 
least those on the order of one minute or so, commonly 
found affecting reflectance measurements made with the 
ISCO spectroradiometer which take at least five minutes 
to compile. 

274 



■•**-■,■ 




Figure 55. This photograph shows the dual radiometer calibration configuration used in 
in the field measurement program. The radiometer on the right is pointed vertically 
to measure sky irradiance. The instrument on the left is pointed downward to measure 
reflected energy from a FIBERFRAX panel on the ground. 



275 



4. Measurements are recorded while viewing FIBERFRAX to 
determine the local inter-calibration between 1% 
irradiance and 15° FOV reflected irradiance. A straight 
line relationship, with the correlation R = 0.95, is 
usually observed in these types of standard measure- 
ments. (On this particular day, intermittent snow and 
rapidly changing cloud patterns caused a marked departure 
from the ideal . ) 

5. Where outcrops could be observed directly the FIBERFRAX 
panel was removed and the double unit (Exotech radio- 
meters) placed on the outcrop. 

6. Most of the data was taken with the double unit assembled 
so that each radiometer was on a tripod. The 2tt 
upward-viewing unit was placed vertically, diffusing 
disks upward. The target unit now changed to a 1° FOV 
was used like a TV camera to view selected targets 

at 

varying distances using the calibrated co-linear 1:1 
telescope as a viewing device. For data recording 
purposes, a 35mm color photo was taken of almost every 
target directly through this telescope. 

7. Software programs were used to reduce the voltage 
output data from each of the eight channels to irradiance 
and radiance values, the ratio of which is hemispherical 
reflectance . This factor is usually lower than those 

of the geometry more normally reported, i.e. bi-direc- 
tional reflectance, which is obtained by using both 
units downward-viewing with the same field-of-view. A 
simple factor, however, relates to numbers. 

8. All reflectance measurements were taken using the 
geometry shown in Figure 56 and calculated to the 
geometry shown in Figure 57 using this factor. 

9. Because of the rapidly changing lighting conditions 
which prevailed during the data collection period, only 
those data acquired during bright sunlit conditions 
were used for data analysis. 



276 





Figure 56 - Radiometer orientation for B/A, hemispherical reflectance measurements. 





Figure 57 - Radiometer orientation for B/A, bi-directional reflectance measurements. 



277 



APPENDIX F 
MULTISPECTRAL AND THERMAL INFRARED DATA ACQUISITION AND PROCESSING 

1.0 DATA ACQUISITION 

1.1 Description of DS-1230/125Q Multi spectral Scanner 

The thermal infrared and multispectral airborne data acquisi- 
tion phase of this program utilized the Daedalus DS-1230/1250 
multispectral scanner system. This scanner system was designed to 
provide the capability to quickly change from a dual-channel quan- 
titative thermal infrared scanner to a full eleven-channel multi- 
spectral scanner. Therefore, it was possible to provide dual- 
channel thermal infrared data during the hours of darkness and 
eleven channels of multispectral data during daylight hours on 
both the eastern and western test sites. 

The complete system consists of the following major com- 
ponents: 

Scan Head & Gyro . The dual -channel scan head contains two 
detector mounts, focusing optics, a dichroic mirror to 
divide the energy beam to the two detector systems, rotating 
assembly consisting of the scanning mirror, sync generator 
slugs and drive motor, and the reference source(s). 

The roll correction system includes an on-head mounted 
military specification vertical gyro assembly. 

Detectors . In this investigation, two 8-14 ym tri-metal 
( Hg , Cd , Te ) detectors were used for the thermal studies. A 
ten-channel spectrometer head and one thermal detector was 
used for other phases of data acquisition. 

The ten-channel spectrometer head contains the detector 
array, solid-state planar diffuse silicon photodiodes which 
cover the .38-1.10 ym region, pre-amplifier electronics, and 
imaging optics which focus the collected energy into the 
detector array. 

Data Recording . In-flight data recording is accomplished by 
employing a wideband Group II FM magnetic tape recorder. 
The tape recorder carries 9200 feet of 1" 14- track and at 
30 ips permits one hour of full multispectral recording. 

Other Components . Other major electronic components which 
are required to complete the system are: Spectrometer 



278 



Control Console, Scanner Control Console, and Power Distrib- 
utor and Reference Source Controller. 

The reference source controller maintains pre-set tempera- 
tures to the calibration sources (blackbody temperature ref- 
erences) located on the scan head. Temperature readout is in 
C° and indicates 0.1 degree. 

The basic operating parameters of the system are as 
follows: 



Operating Wavelength 

Aperture 

Focal Length 

Optical Aperture (effective) 

Scan Rate 

Total Field of View 

Gated Field of View 

Instantaneous Field of View 



Temperature Resolution 

V/H 

Roll Correction 

Reference Sources 



Reference Range 



Temperature Sensor Indicator 
Range 



second 



2.5 mrad 
0.2°C 



.38-14.0 ym 

five- inches 

six-inches 

f/2 

80 scans per 

87°20' 

77°20' 

Infrared: 2.5 or 1.7 
mrad 

Visible: 

Infrared: 

.2 

Total: +10°; Unvig- 
netted: +5° 

Infrared: two con- 
trollable thermal 
blackbodies 

Visible: one fixed 
voltage broadband 
visible/IR light 
source 

Infrared: -10°C to 
+40°C with respect 
to scan head heat 
sink 



Visible: 
1.2 ym 

Infrared: 
+50°C 



,35 - 
-10°C to 



1 .2 Spectral Configurations Used 

In order to provide optimum multispectral data for geologic 
analysis of the tunnel sites, the DS-1250 scanner was configured 
for different spectral recording during the day and night flights. 
The daytime flights utilized one infrared detector and the ten- 
channel spectrometer with the standard dichroic filter. This 
configuration provides the following spectral response for each of 
the eleven channels: 

279 



Channel 

1 
2 
3 
4 
5 
6 



Spectral Region 



.38 - 


.42 ym 


.42 - 


.45 ym 


.45 - 


. 50 ym 


.50 - 


. 55 ym 


.55 - 


.60 ym 


.60 - 


. 65 ym 



Channel 

7 

8 

9 

10 

n 



Spectral Region 



.65 - 


.69 ym 


.70 - 


.79 ym 


.80 - 


.89 ym 


.92 - 


1.10 ym 



8.0 -12.5 ym 



Figure 58 is a cross-section of the scan head showing the 
configuration of detectors and filters for the daytime flights. 

For the night flights it was desired to divide the normal 8- 
14 ym thermal infrared window into two regions, 8-10 ym and 10- 
12 ym, in order to investigate the possibility of discriminating 
rock types on the basis of emissivity differences in these two 
bands. Therefore, a special dichroic filter was manufactured to 
accomplish this division and detectors and optical filters were 
chosen to provide the best possible match in terms of efficiency. 
The resulting efficiency values for the two bands were as follows; 

8-10 ym Region 

Average detector response = 90% 
Average filter transmission = 90% 
Average dichroic reflectance = 99%; or 
.90 X .90 X .99 = 80% efficient . 

10-12 ym Region 

Average detector response = 90% 
Average dichroic transmission = 90%; or 
.90 X .90 = 81% efficient . 

Considering the 50% points of each band, the actual spectral 
coverage was as follows: 

8.2 - 10.2 ym for the nominal 8-10 ym region. 
10.3 - 12.5 ym for the nominal 10-12 ym region. 

Figure 59 is a cross-section of the scan head showing the 
configuration of detectors and filters for the night flight. 

Figure 60 is a graphic representation of the relative spec- 
tral response of each of the detector/filter combinations. 



1 .3 Scanner Operation 

The in-flight operation of the DS-1 230/1 250 multispectral 
scanner system is performed from the master control console. 
This console contains controls for all electrical power to the 



280 



INFRARED DETECTOR 



DEI- 160 SPECTROHIETER 



GYRO 



W^V. 






SYNC SENSORS 



Liitiiiitiitiimi 




77>//y>77?/y//^/y//^ 






1 



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MOTOR 



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Figure 58 - Scanner Configuration - DOT Tunnel Study - Day Flights. 



281 



INFttARED DCTECTORS 




Figure 59 - Scanner Configuration - DOT Tunnel Study - Night Flights. 



282 




WAVELENGTH, ><m 
NOMINAL 8-IO>im COMBINATION 




8 9 10 II 

WAVELENGTH, /um 
NOMINAL I0-I2>im COMBINATION 



12 15 14 



Figure 60 - Relative Spectral Response of Detector/Filter Combinations. 



283 



major system components and for remote control of the magnetic 
tape recorder. The operator's console contains a dual-channel 
oscilloscope for monitoring the video signals from the detectors. 
In the dual channel configuration, the operator continuously 
monitors the output of both detectors. In the eleven-channel 
multispectral configuration the operator has the option of either 
static monitoring of any two channels or automatically sequencing 
through all eleven channels with each channel displayed for 
approximately ten seconds at a time. In all cases, the operator 
monitors the signals from the reproduce heads of the tape re- 
corder so that the signals he sees have already been recorded on 
magnetic tape. In this manner, the operator can be sure that he 
has a good tape recording of the signals from the detectors. 

The initial setup of each channel of the scanner is also 
facilitated by the use of the in-flight monitor scope. The 
operator can see not only the detector output from each scan 
across the terrain, but also the reference sources are temperature 
controlled blackbody radiators for the infrared detectors and a 
calibrated broad spectrum lamp for the spectrometer detector. 
The operator uses the reference sources to establish the optimum 
amplifier gain and DC level for each of the detector outputs in 
order to faithfully record the entire dynamic range of signal on 
magnetic tape. 

All of the amplifier settings are recorded on a flight log 
by the operator for each flight line. In addition to these 
settings, the flight log contains flight line identification, 
time, altitude, speed, and heading information; all of which is 
used during playback to reconstruct the scene viewed by the 
scanner. 



284 



2.0 DATA PROCESSING 

2.1 Description and Operation of DS-1850 Multispectral Ground 
Station 

All of the magnetic tape playback of the data from the 
Tunnel Study multispectral scanner flights was performed on the 
DS-1850 ground station illustrated in Figure 61. This playback 
system is specifically designed to handle data recorded by the 
DS-1250 multispectral scanner and incorporates a number of fea- 
tures to automate the data handling. 

A flow diagram showing the components and processing steps 
involved in the DS-1850 data processor is illustrated in Figure 62, 
The basis of this processing approach, is that the interpre- 
tability of multispectral data can frequently be improved by 
examining ratios of the signals from various channels rather than 
the raw signals themselves. 

The first step in the pre-processor is the formation of 
signals A and B from combinations of any or all of the available 
spectral channels. This is accomplished by first phase adjusting 
each channel to correct any registration errors across channels—' 
which may have been introduced by the tape recorder and then 
calibration of the signal amplitude through the use of the inter- 
nal calibration reference signals to bring all signals to the 
same power reference base. Any combination of spectral channels 
can then be created by activation of a four-position switch for 
each channel on the pre-processor front panel . 

Once signals A and B have been formed, a function switch 
allows them to be transformed into a resultant output signal 
representing either the product AB, the difference A-B, the ratio 
A/B, or the difference ratio (A-B)/B. Since any combination of 
spectral signals can be used to form the signals A and B, the 
flexibility of the system in terms of spectral comparisons which 
can be made is almost unlimited. 

When the desired spectral function is obtained, the output 
signal may either be supplied directly to the DEI-616 printer for 
film recording or to the post-processor, DEI-612, for calibration 
and digitization prior to printing. In the case of ratio, differ- 
ence, or product signals, the post-processor would allow the 

T7 The analysis conducted during this study necessitated the running 
of the taped data many hundreds of times. Stretching of the tape 
occurred creating some registration problems. On future research 
projects of this type a duplicate tape should be made for the 
routine experimentation. 



285 




Figure 61 - The DS-1 850 ground station provides a wide range of functions for processing of 
the analog recorded multispectral data. The unit protruding on the right is the film magazine 
used for making film copy of the imagery. 



286 




a 
■o 



287 



total range of derived values to be divided into eight discrete 
ranges for printing on either black-and-white or color film. 
With careful spectral function selection, this would permit the 
automatic display of desired terrain features in a pre-selected 
density on black-and-white film or as a specified color on color 
film. 

The range of possible outputs varies from a single spectral 
channel printed on 70 mm or five-inch film to a complete set of 
color separations on 70 mm color film, depending upon the desires 
of the console operator. 

The DEI-616 printer records the signal data by means of a 
fiber optics-cathode ray tube. Permanent records are obtained on 
either direct print paper or photographic film. The printer has 
a removable film cassette which provides either 70 mm or five- 
inch film on an interchangeable basis. The fiber optics face 
plate transmits the light beam from the inner phosphor coating of 
the CRT to the polished outer surface with negligible diffusion. 
This permits a sharp image to be exposed on paper or film which 
moves continuously in close contact with the face of the CRT. 

Selectable single or dual channel operation of the printer 
is provided for by an analog multiplexer and split screen re- 
cording. This feature permits two channels of multiband data to 
be recorded side-by-side on five-inch film. An important addi- 
tional feature is rectilinearized (tangential) scale correction 
of the sweep to minimize image distortion. 



2.2 Multispectral Processing Algorithms 

One of the processor's primary functions is to establish 
repeatable, calibrated video signal levels from the ground scene 
relative to known voltage references. If the video is from a 
quantitative line scanner which contains two calibrated thermal 
reference sources, the output voltages from the thermal sources 
provide the calibration standardization and all video levels can 
be assigned absolute temperatures. If the scanner does not 
contain calibrated thermal sources, the video is compared to 
preset calibratation voltages within the processor to yield repeat- 
able relative video thermal assignments which are not directly 
related to an absolute temperature scale. 

In addition to providing calibrated video, the signal pro- 
cessor also includes several methods for enhancing the presen- 
tation of the ground scene video information. These enhancements, 
when used properly, can help speed data interpretation, emphasize 
important details within the imagery especially for untrained 
observers, and improve understandability of data presentation in 

288 



reports. The signal processor is primarily a digital device 
which generates several calibrated levels within the full refer- 
ences voltage range in the 8 Level mode of processing. Each 
calibrated level prints as a uniform gray level on film (eight 
levels were chosen as a practical maximum number of gray scales 
which can be distinguished when widely separated on film). An 
ISOLEVEL mode prints out a single one of the calibrated levels as 
black on a white background; for example, one which might repre- 
sent all areas between 32°C and 33°C. A CONTOUR mode prints dark 
for 20 micro-seconds after transition between any adjacent levels, 
resulting in contour lines of constant temperatures. The isolevel 
or contour line can be superimposed upon reduced-amplitude normal 
video in the ANALOG mode of operation to provide a spatial refer- 
ence background. The available modes are summarized below with 
correspondence between DIGITAL and ANALOG modes indicated: 

SIGNAL PROCESSOR MODES 

Digital Modes Analog Modes 

8 Level Analog 

Isolevel Anal/Iso 

Contour Anal/Ctr 

Usefulness of the 8-LEVEL, ISOLEVEL, and CONTOUR modes 
depends upon the character of the input video signal since too 
many transitions between levels may destroy the continuity of the 
enhanced presentation. Thus, it is yery important that the 
operator recognize the types of video and the processor modes and 
settings which are likely to yield the most useful results. 

The DEI-612 signal processor is also designed to combine two 
video signals through an analog processor that performs such 
functions as AB, A/B , (A-B/B), A-B, and B-A. 

Many combinations of processor mode and analog function 
algorithms were used on the DOT Tunnel data from both test sites. 
In general, it was found that the 8-level and isolevel modes were 
most useful with single channel thermal infrared data, while most 
of the multi spectral ratio data were displayed in analog image 
form. 

The contour mode proved to be especially useful in analyzing 
patterns of linears on the test sites. 

The following tables are a listing of the various types of 
processing performed on the multi spectral and thermal data during 
the analysis and interpretation. 



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301 



APPENDIX G 



AIRBORNE ELECTROMAGNETIC SYSTEM (DIGHEM) 



1.0 INTRODUCTION 

The name, DIGHEM is an acronym derived from "digital -helicopter- 
electromagnetic" . Basically, DIGHEM is an audio-frequency (918 Hz), 
double-dipole electromagnetic system consisting of a transmitter- 
receiving system mounted in a 30 foot (9m) fiberglass tube commonly 
called a "bird." The transmitter coil is located at one end of the 
bird and mounted vertically with its axis parallel to the flight 
direction. The three receiver coils are mounted at the opposite end 
of the bird, at right angles to each other as shown in Figure 63. A 
signal broadcast by the transmitter may be affected by differences in 
conductivity of the near-surface material of the earth and eddy 
currents generated. The receiver coils measure the three mutually 
perpendicular space components of the anomalous field. 



A DIGHEM survey (Figure 64) of 50 line-miles was flown between 
October 9 and October 22, 1975 over the East River Mountain and Walker 
Mountain tunnel sites in Virginia and West Virginia. 

TRANSMITTER 
COIL (918 hz) 



3 RECEIVER 
COILS 




Figure 63 - Transmitter and receiving coil orientation as mounted in the 30-foot (9m) muiticoil bird. 



302 




Figure 64 - Dighem system flying an electromagnetic survey 



303 



2.0 SURVEY DESCRIPTION 

The survey was conducted with an Alouette II jet helicopter, C- 
GNQX, which flew with an average airspeed of 60 mph and EM bird height 
of 130 feet. Ancillary equipment consisted of a Barringer Research 
Limited AM-104 magnetometer with its bird at an average height of 180 
feet, a Bonzer radaraltimeter, Geocam sequence camera, 60 hz monitor, 
MFE eight-channel hot pen analog recorder, and a Geometries G-704 
digital data acquisition system with a Facit 4070 punch paper tape 
recorder. The analog equipment recorded six channels of EM data at 
approximately 900 hz (or, alternatively, five channels of EM and one 
of sferics), magnetics and radaraltitude. The digital equipment 
recorded the magnetic field to an accuracy of one gamma. 

The flight record is a roll of chart paper which moves through 
the recorded console at a speed of 1.5 mm/sec. This provides a ground 
scale on the flight record in feet/mm which is approximately equal to 
the helicopter flight speed in mph. Thus, for example, the ground 
scale of the flight record is approximately 70 feet/mm when the heli- 
copter flies at 70 mph. 

The flight record consists of eight channels of information as 
follows, from top to bottom: 



Channel 

1 whaletail null coil quadrature 

2 fishtail null coil quadrature 

3 maximum-coupled coil inphase 

4 maximum-coupled coil inphase 
5-/ maximum-coupled coil quadrature 

6 maximum-coupled coil quadrature 

7 radaraltitude 

8 magnetometer: 1 gamma/step 



Time 


Constant 


4 


sec 


4 


sec 


1 


sec 


4 


sec 


1 


sec 


4 


sec 


1 


sec 


1 


sec 



Scale 
units /mm 

2 ppm 
2 ppm 
5 ppm 
2 ppm 
5 ppm 
2 ppm 
10 feet 
2.5 gamma 



Noise— 



ppm 

ppm 
ppm 
ppm 
ppm 
ppm 



In addition, three fiducial markers are used between the channels, 
as follows: 



]_/ The quoted noise levels are generally valid for wind speeds up to 
~ 20 mph. Higher winds may cause the system to be grounded be- 
cause excessive bird swinging produces control difficulties in 
piloting the helicopter. The swinging results from the 50 square 
feet of area which is presented by the bird to broadside gusts. 



y A "sferic" detector replaced this channel on some flights for pur- 
poses of monitoring the inflight ambient noise, e.g. from distant 
thunder storms. 



304 



Fiducial Occurrence 

60-Hz marker occurs only over power lines 

camera fiducial s occurs regularly at 3 mm 

intervals on every line 

navigator fiducial s occurs discontinuously on 

eyery line 

The 60-Hz fiducial identifies anomalies generated by power lines, 
allowing them to be deleted from the EM map. 

The navigator fiducial marks represent points on the ground which 
were recognized by the aircraft navigator. These are the initial base 
points for flight path recovery. The flight line begins with a single 
navigator fiducial. This is followed by a series of unevenly-spaced 
fiducials moving right-wards along the record, which is in the direction 
of the flight. The end of the line is flagged by a string of three 
navigator fiducial marks. 

The camera fiducial marks indicate each point where a photograph 
was taken. These photographs are used to provide accurate photo-path 
recovery locations for the navigator fiducials, which are then plotted 
on the geophysical maps to provide the track of the aircraft. 

The navigator fiducial locations on both the flight records and 
flight path maps are examined by a computer for unusal helicopter speed 
changes. Such changes often denote an error in flight path recovery. 
The resulting flight path locations therefore reflect a more stringent 
checking than is provided by standard flight path recovery techniques. 



305 



3.0 DATA PRESENTATION 

3.1 The Three Conductor Models 

DIGHEM anomalies may be interpreted according to three con- 
ductor models, as follows: 

Vertical dike (half plane) 

The vertical dike is the most suitable representation of 
steeply-dipping bedrock conductors. For base metal 
exploration, EM anomalies are plotted on a map and are 
interpreted according to this model. The three re- 
ceiver coils of DIGHEM allow correction for the response 
when the flight line crosses a conductor at an oblique 
angle. 

Horizontal sheet (whole plane) 

The horizontal sheet is suitable for flatly-dipping 
thin layers of conductive clay or lake silt. For the 
normal base metal survey programs, the conductance and 
depth values are given in the anomaly list appended to 
the rear of the survey report, but do not appear on the 
EM map. These values are to be viewed with caution 
unless it is known that a horizontal sheet is a fair 
representation of the conductors. It is a highly 
specialized model with a limited application. 

Conductive earth (half space) 

The conductive earth model is suitable for f lay-dipping, 
thick bedrock conductors, saline water-saturated sedi- 
mentary formations, thick conductive overburden and 
geothermal zones. The resistivity and depth values may 
be contoured for applications involving resistivity 
mapping. The following section describes the con- 
ductive earth model in detail because it was used for 
the tunnel site survey. 



3.2 Resistivity Mapping with DIGHEM 

DIGHEM has encountered areas of widespread conductivity 
while surveying for base metals. Under such conditions, anom- 
alies can be generated by changes of only 20 feet in survey 
altitude, as well as by changes in conductivity. Figure 65 
shows a DIGHEM flight record where inphase and quadrature channels 
are continuously active; local peaks reflect either increases in 



306 




Sout^ 



N ••«-*)» 



Figure 65 - Dighem flight record. Local peaks reflect either increases In conductivity or decreases in altitude. 



307 



conductivity or decreases in altitude. For such survey areas, 
apparent resistivity maps should be produced from the airborne 
data. The advantage of the contoured map is that anomalies 
caused by altitude changes are eliminated, and the contours 
reflect only the conductive anomalies. In areas of considerably 
widespread conductivity, the conventional EM map may be prac- 
tically useless. Contoured resistivity maps improve the inter- 
preter's ability to distinguish between conductive trends in the 
bedrock and those patterns typical of conductive overburden. The 
computer software uses a conductive earth algorithm derived from 
Frischknecht. 

The inputs to the DIGHEM algorithm are the inphase and 
quadrature ppm of the maximum-coupled coil. The outputs from the 
algorithm are resistivity in ohm-meters and distance from the EM 
bird. The radar altitude is subtracted from this distance to 
provide a depth below surface to the conductive earth. Because 
depth is a parameter derived from the analysis, the formulation 
is not a half-space algorithm in the strictest sense. In actual 
fact, it represents a two-layer case where the resistivity of the 
upper layer is assumed to be infinite, and the resistivity of the 
lower layer is that of the conductive earth (Figure 66). 

Figure 67 presents the results of a DIGHEM survey for base 
metals. Resistivity contours in ohm-meters are superimposed on 
the EM anomaly photomosaic. The EM anomaly patterns are mis- 
leading because they suggest the existence of specific conductor 
axes which are indicative of steeply-dipping conductors. In 
reality, broad patterns such as those of Figure 65 imply that the 
induced current flow paths were primarily horizontal rather than 
steeply-dipping. Resistivity contours provide a truer repre- 
sentation of the conductive environment, and indicate that the 
ENE-striking 30 ohm-meter band in the east-half of Figure 67 is 
caused by bedrock conduction. This band strikes perpendicular to 
the drainage in an area of moderately high relief. 



3.3 Magnetics 

The digitally recorded magnetometer data from the airborne 
survey has a usable resolution of approximately five gammas. The 
digital tape is processed by computer to yield a standard total 
field magnetic map contoured at 25 gamma intervals. 



308 




/k>k 




77777. 

infinite resistivity 




^o/cu/oted depth 



mTi 



interpreted resistivity 



Figure 66 - The conductive earth model is actually a two-layer case where the upper layer has an infinite 
resistivity. The calculated depth d is the difference between the interpreted height h and the radar altitude a. 



309 
















Figure 67 - Apparent resistivity map witii contours in ohm-meters. The survey was flown with a Dighem electromagnetic system 
operating at 900Hz. The arrows identify the flight line of Figure 65. 



310 



APPENDIX H 

COMMERCIALLY AVAILABLE RADAR AND AIRBORNE 
ELECTROMAGNETIC SURVEY SERVICES 

1.0 RADAR 

Should it be desirable or necessary to obtain new radar imagery 
of a specific area, three organizations in the United States provide 
commercial services for radar imagery acquisition. These are: 

ERIM 

P.O. Box 618 

Ann Arbor, Michigan 48107 

Tel: 313-994-1200 

ERIM system has a dual frequency (X and L bands) synthetic apera- 
ture radar in a DC-3 aircraft. The system has a capability of trans- 
mitting in either horizontal or vertical polarization and receiving in 
both vertical and horizontal polarization for a total of four channels 
of data. 

Aero Services Division 

Western Geophysical Company of America 

4219 Van Kirk Street 

Philadelphia, Pennsylvania 19135 

Tel: 215-533-3900 

Aero Services has an exclusive arrangement with Goodyear Aero- 
space Corporation to use their synthetic aperature, X-band radar 
system for commercial purposes. This system, mounted in a Caravel le 
twin-jet aircraft, can map a swath of terrain 20 nautical miles (36 km) 
wide with a uniform resolution of about 40 feet (16 m) throughout the 
imagery. 

Motorola Aerial Remote Sensing, Inc. 
4039E. Raymond St. 
Phoenix, Arizona 85040 
Tel: 602-244-5751 

Motorola's AN/APS-94D, brute-force, radar system is flown commer- 
cially in a Grumman Gulfstream aircraft. The depression angle on this 
system is readily changeable which is of advantage for areas of differ- 
ent relief characteristics. 



311 



Goodyear Aerospace is the repository for Air Force radar imagery from 
certain programs. Within this repository there are approximately six 
million square miles of radar imagery covering the United States. 
Most of this radar imagery is available to non-military organizations. 
The radar imagery that is available is at four different resolutions 
and scales. (Resolution-10- , 20-, 40-, 50-foot, and scales from 
1:100,000 to 1:600,000). The military has recently declassified 10- 
foot resolution radar imagery at a scale of 1:100,000 of the United 
States. 

Goodyear Aerospace has information pertaining to this radar 
imagery catalogued for retrieval by a number of categories including 
geographic coordinates. When a request is received for a certain 
area, the geographic coordinates and a radius is entered into a com- 
puter. The computer will print out information for all coverage over 
this coordinate, such as flight number, pass number, start and end 
coordinates, and coded information, for resolution and scale. The 
computer printout is then mailed to the requester with an explanation 
on how to use it. The requester will have to plot the coordinates 
from the printout and determine which pass or passes of radar imagery 
cover his/her area of interest. The requester will then send a letter 
to the address above requesting the pass/ passes that cover their area. 
A statement explaining what the imagery will be used for should accompany 
the request. 

There is a charge for reproduction of $40.00 per pass; for this 
fee a contact transparency and a paper print are reproduced and 
shipped to the requester, usually within a week. This reproduction - 
depending on resolution and scale of the radar imagery - will cover 
between 100 and 2500 square miles. The size of the reproduction will 
be approximately 5" x 15". Additional prints and enlargements are 
available upon request. Price will be provided when requested. 

A 10" X 13" reproduction of a wall map showing coverage of the 
United States also may be obtained upon request. 



312 



2.0 ELECTROMAGNETIC SURVEYS 

There are a number of companies that provide airborne electro- 
magnetic surveys. The capabilities of the different systems used vary 
and should be thoroughly evaluated for the job requirement before 
contracting. Table 19 (after Hood, 1974) lists a series of service 
companies with such equipment and provides some guidance as to systems 
characteristic and sensitivity. 



313 



Table 19 Chart of Electromagnetic System Operating Parameters 



EM SYSTW 

T« Rx 

Flight 

nim 


MANUFACTURER/ 
CONTRACTOR 
- Survey 
Platform 


NORMAL 
HEIGHT 

Tx 


SURVEY 
IN METRES 

Ri 


COIL 
SEPARATION 


FREO. 
(HJ) 


MEASURE 
I/P-In Phase 
0/P-Out of 

Phase 


NOISE 
LEVEL in 
parts per 
million 


RESPONSE 

FROM 

OVERBURDEN 

(In Canada) 


♦6 --6 

Vertical 
Coaxial 
Rioid Coupled 


Barringer 
- Helicopter 


30 ■ 


30 • 


9.1 or 4.9m 


900 


I/P and O/P 


2 ppm 


Small 


Kenting 
- Canso 


45 m 


4S ■ 


25 m 


390 


I/P and O/P 


15 ppm 


Snail 


Northway 
LHEM 200 

LHEM 250 


......... 

30 m 
30- 


30 • 
30 * 


9.1 m 
9.1 m 


4000 
1000 


I/P and O/P 
I/P and O/P 


5 ppm 
5 ppm 


Moderate 

Snail 


Sander 

- helicopter 


40 m 


40 m 


7 m 


500 


I/P and O/P 


♦1 ppm I/P 
•.5 ppm O/P 


Small 


Scintrex 
Helicopter 
HEM 701 


30 ■ 


30 m 


9.1 m 


1600 


I/P and O/P 


3 ppm 


Small 


Multicoil Room 
Rigid Coupled 


Barringer 
- Helicopter 

Aerodat 

Dighcm 




30 • 


30 b 


9.1 m 


914 


I/P and O/P 


2-4 ppm 


Uha1e Tail 
- large 
Fish Tail A 
Coaxial- 
Small 


0-^ 

Min. Coupled 
Towed Bird 


Northway 
LHEM 210 


137 m 


70 ■ 


130 m 


400 A 

2300 


O/P 


840 ppm 


Large 


McPhar 
F-400 

McPhar 
F-500 


130 m 
130 ■ 


40 m 
40 • 


120m; 60m 
behind 1 
90m below 

120m; eon 
behind A 
90m below 


340 and 
1070 Hz 
-time 
shared 
340. 
1070 A 
3450 
1 


O/P 
O/P 


500 ppm 
500 ppm 


Medium 
Mediun 


Time Domain \J 
Towed Bird 


Barringer INPUT 

Geoterrex-Canso 

Ouestor-Canso 
i Skyvan 


120 m 


50 m 


75m behind 
and 75m 
below 


286 pulsed 
H sine waves 
per sec. 


Transient 
at 6 
intervals 




Larqe on 
Channel 1 
decreasing 
to zero on 
other 
channels 


Hi no Hounted 
na>. Coupled 


Geoterrex Otter 

Kenting Otter 

SOOUEM Cessna 
305 

Scintrex- 
Tridem 


45 m 

40 m 

«0 m 


45 m 

40 m 
60 •) 


19 m 

11 m 
17.7 m 


320 

694 

500 
2000 
^ 8000 


I/P and O/P 

I/P and O/P 

I/P and O/P 
3 freq. 
simultaneously; 


20 ppm 

30 ppm 
20-40 ppm 


Small 

Small 

Small 

Moderate 

Large 


Rotary Field 


AS EM 
(Sweden) 

- two plane 


80 m 


80 m 


300 m 


880 


Relative 
I/P and O/P 


ir 


Fairly 
Large 


Ground ^ir 
Loop (3) 


Scintrex- 
Turair 11 


Ground 
Loop 


60 m 


Several 
kilometres 


200 i 
400 


Field Strength 
Ratio and 
Phase Gradient 


O.IT 


Variable 


Very Low 
Frequency 
(VLF) 


Barringer 
Radiophase 
and E-Phase 


30 - 
300 m 


30 - 

300 m 


OD 


15 KHZ 

to 
25 KHz 


I/P and O/P 




Large 


Geonics 
EM- 18 


60 - 
90 m 


60 - 
90 m 


CO 


15 r.t^z 

to 
25 KHz 


I/P and n/P 


o.sr 


L*rae 


McPhar 
KEM 


30 - 
300 m 


30 - 
300 m 


CO 


15 KHz 

to 
25 KHZ 


nip Annie 

and 
Amplitude 


0.6 V at 

sensor 

coils 


Lame 


AFMAG ^ ^ 


McPhar 
AF-4 


30 - 
300 m 


30 - 
300 m 


0} 


140 A 
500 Hz 


Tilt Anale 

essentially 

I/P 


,0 . 2° 


Small 



314 



APPENDIX I 
ACQUISITION OF EXISTING REMOTE SENSOR DATA FROM FEDERAL AGENCIES 



Several federal government agencies acquire remote sensor data 
which have been made available to the public for a nominal cost. 
These data consist primarily of aerial photography and satellite 
imagery, but limited amounts of radar thermal and multi spectral scanner 
imagery are also available. Many potential users who could benefit 
from the services are not aware of the availability of the different 
types of imagery and the procedures for acquiring these data. Con- 
sequently, considerable detail is presented about the data and ser- 
vices provided. Much of the following section has been extracted ver- 
batim from an EROS publication. 



1.0 EROS DATA CENTER 

Although several outlets exist for government acquired remote 
sensor data, the largest is the EROS (Earth Resources Observation 
System) Program of the U.S. Department of Interior. This program, 
administered by the Geological Survey, maintains a major storage and 
retrieval facility in Sioux Falls, South Dakota. 

They operate a computerized data storage and retrieval system 
which is based on a geographic system of latitude and longitude, 
supplemented by information about image quality, cloud cover, and type 
of data. A customer's inquiry about availability of remotely sensed 
data may be about a geographic point location or a rectangular area 
specified by latitude and longitude corner coordinates. Depending on 
customer requirements, a computer geographic search will print out a 
listing of available imagery and photography from which the requester 
can make a final selection. Receipt of a pre-paid order initiates 
processing. To place an order, to inquire about the availability of 
data, or to establish a standing order, contact: 

User Services Unit 

EROS Data Center 

Sioux Falls, South Dakota 57198 

Phone: 605-594-6511, extension 151 

FTS: 605-594-6151 



1.1 EROS Data Reference Files 

EROS Data Reference Files have been established throughout 
the United States to maintain microfilm copies of the data avail 
able from the Data Center and to provide guides to assist the 



315 



visitor in reviewing and ordering data. This allows the visitor 
to view microfilm copies of the data before placing an order. 
Applications assistance by scientists is not provided at EROS 
Data Reference Files. The table below lists the address, tele- 
phone number, and hours of operation of each of the 11 Data 
Reference Files. 



EROS Data Reference File 
Public Inquiries Office 
U.S. Geological Survey 
108 Skyline Building 
508 Second Avenue 
Anchorage, Alaska 99501 
Phone: 907-277-0577 
Hours: 9:00-5:30 

EROS Data Reference File 
Public Inquiries Office 
U.S. Geological Survey 
Room 7638, Federal Building 
300 North Los Angeles Street 
Los Angeles, California 90012 
Phone: 213-688-2850 
Hours: 9:30-4:00 



EROS Data Reference File 
Public Inquiries Office 
U.S. Geological Survey 
Room 678, U.S. Court House 

Building 
West 920 Riverside Avenue 
Spokane, Washington 99201 
Phone: 509-456-2524 
Hours: 9:00-4:30 

EROS Data Reference File 
Topographic Office 
U.S. Geological Survey 
900 Pine Street 
Rolla, Missouri 65401 
Phone: 314-364-3680 
Hours: 8:00-5:00 



EROS Data Reference File 
State Topographic Office 
Lafayette Building, Koger Office 

Center 
Tallahassee, Florida 32304 
Phone: 904-488-2168 
Hours: 8:15-5:15 



EROS Data Reference File 
Water Resources Division 
U.S. Geological Survey 
975 West Third Avenue 
Columbus, Ohio 43212 
Phone: 614-469-5553 
Hours: 8:00-4:30 



EROS Data Reference File 
University of Hawaii 
Department of Geography 
Room 31 3C, Physical Science 

Building 
Honolulu, Hawaii 96825 
Phone: 808-944-8463 
Hours: 8:00-4:00 



EROS Data Reference File 
Water Resources Divison 
U.S. Geological Survey 
Room 343, Post Office and 

Court House Building 
Albany, New York 12201 
Phone: 518-474-3107 or 6042 
Hours: 8:00-4:30 



EROS Data Reference File 

U.S. Geological Survey 

5th Floor 

80 Broad Street 

Boston, Massachusetts 02110 

Phone: 617-223-7202 

Hours: 9:00-5:00 



EROS Data Reference File 
Bureau of Land Management 
729 NE. Oregon Street 
Portland, Oregon 97208 
Phone: 503-234-3361, ext.4000 
Hours: 8:00-4:00 



316 



EROS Data Reference File 
Maps and Surveys Branch 
Tennessee Valley Authority 
20 Honey Building 
311 Broad Street 
Chattanooga, Tennessee 37401 
Phone: 615-755-2133 
Hours: 8:00-4:00 



1.2 EROS Applications Assistance Facilities 

The EROS Data Center also operates several Applications 
Assistance Facilities which maintain microfilm copies of data 
archived at the Center and provide computer terminal inquiry and 
order capability to the central computer complex at the EROS Data 
Center. Scientific personnel are available for assistance in 
applying the data to a variety of resource and environmental 
problems and for assistance in ordering data from the Data Center. 

The Applications Assistance Facilities should be contacted 
by phone or mail in advance, so that suitable arrangements can be 
made for a visit. 



EROS Applications Assistance 

Facility 
U.S. Geological Survey 
Room 202, Building 3 
345 Middlefield Road 
Menlo Park, California 94025 
Phone: 415-323-2727 
Hours: 8:00-4:15 

EROS Applications Assistance 

Facility 
EROS Data Center 
U.S. Geological Survey 
Sioux Falls, South Dakota 57198 
Phone: 605-594-6511 
Hours: 8:00-4:30 



EROS Applications Assistance 

Facility 
U.S. Geological Survey 
Room 8-210, Building 1100 
National Space Technology 

Laboratories 
Bay St. Louis, Mississippi 39520 
Phone: 610-688-3472 
Hours: 8:00-4:30 

EROS Applications Assistance 

Facility 
University of Alaska 
Geophysical Institute 
College, Alaska 99701 

(Fairbanks) 
Phone: 907-479-7558 
Hours: 8:00-5:00 



317 



EROS Applications Assistance 

Facility 
HQ Inter-American Geodetic 

Survey 
Headquarters Building 
Drawer 934 

Fort Clayton, Canal Zone 
Phone: 83-3897 
Hours: 7:00-3:45 

EROS Applications Assistance 

Facility 
U.S. Geological Survey 
Room 2404B, Building 25 
Federal Center 
Denver, Colorado 80225 
Phone: 303-234-4879 
Hours: 8:00-4:30 



EROS Applications Assistance 

Facility 
U.S. Geological Survey 
Room 5017, Federal Building 
230 North First Avenue 
Phoenix, Arizona 85025 
Phone: 602-261-3188 
Hours: 8:00-5:00 

EROS Applications Assistance 

Facility 
U.S. Geological Survey 
1925 Newton Square East 
Reston, Virginia 22090 
Phone: 703-860-7868 
Hours: 8:00-4:15 



and circles the 

per day. Each 
From such a vantage 
except for the 
A unique feature 
it views the 
at the Equator, 



1.3 LANDSAT (Earth Resources Technology Satellite) Data 

The first Earth Resources Technology Satellite, ERTS-1 (now 
re-named LANDSAT-1), was launched July 23, 1972. LANDSAT-2 was 
launched on January 22, 1975. LANDSAT flies in a circular orbit 
570 miles (920 km) above the Earth's surface 
Earth eyery 103 minutes, or roughly 14 times 
daytime orbital pass is from north to south, 
point, each LANDSAT can cover the entire globe, 
poles, with repetitive coverage every 18 days, 
of the satellite, because of the orbit, is that 
Earth at the same local time, roughly 9:30 a.m. 
on each pass. The sensors on board the spacecraft transmit 
images to NASA receiving stations in Alaska, California, and 
Maryland either directly or from data stored on tape recorders. 
The data are converted from electronic signals to photographic 
images and computer compatible tapes at NASA's Goddard Space 
Flight Center (GSFA) in Greenbelt, Maryland. Master reproducible 
copies are flown to the EROS Data Center in Sioux Falls, South 
Dakota, where images are placed in the public domain, and where 
requests for reproductions are filled for the scientific com- 
munity, industry, and the public at large. Because of the experi 
mental nature of the satellite and the limited capabilities of 
NASA ground processing equipment at Greenbelt, approximately 30 
days are required from the time the signals are first received on 
the ground to the time that the data are available to the public 
at the EROS Data Center. 



318 



LANDSAT presently carries three data acquisition systems: 
(1) a multi spectral scanner (four spectral bands), (2) a return 
beam vidicon (RBV) or television system, and (3) a data collec- 
tion system (DCS) to relay environmental data from ground-based 
data collection platforms (DCP's). The mul tispectral scanner, or 
MSS, is the primary sensor system and acquires images of 111 
miles (185 km) per side in four spectral bands in the visible and 
near-infrared portions of the electromagnetic spectrum. These 
four bands are: 

Band 4, the green band, 0.5 to 0.6 micrometers, emphasizes 
movement of sediment laden water and delineates areas of 
shallow water, such as shoals, reefs, etc.; 

Band 5, the red band, 0.6 to 0.7 micrometers, emphasizes 
cultural features; 

Band 6, the near-infrared band, 0.7 to 0.8 micrometers, 
emphasizes vegetation, the boundary between land and water, 
and landforms; and 

Band 7, the second near-infrared band, 0.8 to 1.1 micro- 
meters, provides the best penetration of atmospheric haze 
and also emphasizes vegetation, the boundary between land 
and water, and landforms. 

An analysis of the four individual black-and-white images or 
the false-color infrared composite images often permits scien- 
tists to identify and inventory different environmental phenomena, 
such as distribution and general type of vegetation, regional 
geologic structure, and areal extent of surface water. The 
repetitive (9 or 18 days) and seasonal coverage provided by 
LANDSAT imagery is an important new tool for the interpretation 
of dynamic phenomena. It should be noted that because of the 
Earth's rotation and the fact that the image is created by an 
optical-mechanical scanner, ERTS MSS images are parallelograms, 
not squares. The sides are parallel to the orbital track of the 
satellite on the Earth's surface. RBV images have a square 
format because the image is acquired instantaneously. 

The arbitrary forward overlap between consecutive LANDSAT 
images is approximately ten percent. The sidelap between ad- 
jacent orbits ranges from fourteen percent at the Equator to 
eighty-five percent at the 80° parallels of latitude. 

Latitude and longitude tick marks are depicted at 30-minute 
intervals outside the image edge. These geographic reference 
marks are annotated in degrees, minutes, and compass direction. 
A 15-step gray-scale tablet is exposed on every frame of LANDSAT 
imagery as it is produced. This scale is used to monitor and 



319 



control printing and processing functions and to provide a refer- 
ence for analysis related to a particular image. The annotation 
block directly over the gray scale contains data that give the 
unique image identification, the geographic location, and the 
time (with respect to Greenwich mean time) an image was acquired. 

If you wish to order a single black-and-white image, it is 
best to order band 5. This band usually gives the best general - 
purpose view of the Earth's surface. By ordering a complete set 
of black-and-white images from all four bands, however, you can 
see how the same area differs in appearance when filtered to 
green, red, and near-infrared wavelengths. MSS false-color 
composites are available as standard products. An MSS false- 
color composite image is generally created by exposing three of 
the four black-and-white bands through different color filters 
onto color film. On these false-color images, healthy vegetation 
appears bright red rather than green; clear water appears black; 
sediment- laden water is powder blue in color; and urban centers 
often appear blue or blue-gray. MSS false-color composite images 
which have not already been prepared can be ordered from the Data 
Center but carry a one-time initial preparation charge of $50, 
not including the cost of any products ordered from the resulting 
composite. 

A set of LANDSAT images has been prepared for the conter- 
minous United States. The 470 scenes required to cover the 
United States are available in a single black-and-white (band 
5), all four bands of black-and-white, or high-quality color 
composites. The scenes selected were chosen on the basis of 
quality, optimum time of year (generally spring or summer), and 
minimum cloud cover. 

LANDSAT data in digital form are available as Computer 
Compatible Tapes (CCT). The tapes are standard one-inch-wide 
(12.7-mm) magnetic tapes and may be requested in either seven- or 
nine-track format at 800 or 1,600 bpi. Four CCT's are required 
for the digital data corresponding to one LANDSAT image. The 
data for the four bands are interleaved among the four tapes 
thereby necessitating all tapes to complete a set. The cost of 
one set (one LANDSAT image) is $200. 



1.4 Skylab Data 

The NASA Skylab Program consisted of one unmanned and three 
manned missions. The unmanned space vehicle was placed in orbit 
in February 1973. The manned missions were Skylab 2, launched on 
May 22, 1973, and recovered on June 22, 1973; Skylab 3, in orbit 



320 



from July 28 to September 25, 1973; and Skylab 4, launched on 
November 16, 1973, and recovered on February 8, 1974. 

The spacecraft traveled in an orbit 270 miles (430 km) above 
the Earth and acquired photography, imagery, and other data of 
selected areas between latitudes 50°N. and 50°S. The data 
covered a number of scattered test sites selected to support 
Earth resources experiments. The photography, however, does not 
provide complete, cloud- free, and systematic coverage of the 
Earth's surface between 50°N. and S. latitudes. 

The Skylab Earth Resources Experiment Package (EREP) con- 
sisted of six remote- sensing systems and was designed as a space- 
borne facility to be used by the scientific conmunity. Only two 
of the systems are of interest for tunnel site investigations; 

S190-A - Multi spectral Photographic Camera. A six camera array 
was designed to provide high-quality photography of a wide variety 
of phenomena on the Earth's surface. Each camera used 70 rmi film 
and was a six-inch (152-mm) focal length lens. The films used 
were filtered black-and-white, color, and false-color infrared. 
The area covered by each image of this system is 90 by 90 miles 
(144 by 144 km). 

S190-B - Earth Terrain Camera. A single, high resolution Earth 
terrain camera was selected to provide high-resolution photography 
for scientific study. It used five-inch (127-mm) film and an 
eighteen-inch (457-mm) focal length lens. Various black-and- 
white, color, and false-color infrared films were used in the 
camera. The area covered by each frame of this system was 60 by 
60 miles (96 by 96 km). 



1.5 NASA Aerial Photography 

NASA aerial photography is the product of aerial surveys 
carried out by the NASA Earth Resources Aircraft Program. The 
program is directed primarily at testing a variety of remote- 
sensing instruments and techniques in aerial flights generally 
over certain pre-selected test sites within the continental 
United States, but also includes sites in a few foreign areas. 

Aerial photography is available in a wide variety of formats 
from flights at altitudes of a few thousand feet (1,000 m) up to 
U-2 and RB-57F flights at altitudes above 60,000 feet (18,000 m). 
The high-altitude photography is generally available on a nine- by 
nine-inch (23- by 23-cm) film format at approximate scales of 
1:120,000 and 1:60,000. In general, each high-altitude frame of 
nine-inch (23-cm) film format photography at 1:120,000 scale 
shows an area approximately 15 miles (24 km) on a side. 

321 



Aerial photography is available in black-and-white, color, 
or false-color infrared. Since these data are acquired at 
relatively low altitudes, ground features such as roads, farms, 
and cities are easily identifiable. Cloud cover is present in 
some photographs, and NASA aerial photographic coverage is not 
available for all areas of interest. Some electronic data from 
the more sophisticated research sensors on the aircraft may also 
be obtained through the Data Center. These data, however, are of 
limited areas and long delivery times must be expected. 



1 .6 Aerial Mapping Photography 

Aerial photography during the past 25 years was acquired by 
the U.S. Geological Survey and other Federal Government agencies 
for mapping of the United States. The photography is black- 
and-white and has less than five percent cloud cover. 

Depending on the planned use of the photographs, the aerial- 
survey altitude ranged from 2,000 feet (600 m) to 40,000 feet 
(12,000 m) . The basic film format is nine by nine inches (23 by 
23 cm) and shows areas from three to nine miles (4.8 to 14.4 km) 
on a side depending on the scale of the photograph. 

Because of the large number of aerial photographs necessary 
to show an area on the ground, the photographs have been indexed 
by mounting a series of consecutive and adjacent overlapping 
photographs to create a mosaic of photographs of a specified 
area. These aerial photographic mosaics are referred to as 
"photo indexes" and allow for rapid identification of photographic 
coverage of a specific area. Presently, some 43,000 photo indexes 
are available at the Data Center. To order aerial photography 
from the Data Center, it is necessary that you initially order a 
photo index of your area of interest to determine the specific 
aerial photography needed. 

Should you have difficulty in placing an inquiry or order, 
need assistance in selection of data, or have questions regarding 
your order or additional services, you may write or call: 

Customer Relations Unit 

EROS Data Center 

Sioux Falls, South Dakota 57198 

Phone: 605-594-6511, extension 151 

FTS: 605-594-6151 

Allow a minimum of two to three weeks for delivery of all 
orders. A longer time may be required for the production of 
computer compatible tapes or the completion of yery large or 
complex orders. 

322 



1 . 7 The Geographic Search and Inquiry System 

Requests for information about imagery of a specific area 
will initiate a computerized geographic search. The search can 
be initiated by mail, visit, or phone, to either the EROS Data 
Center or one of the EROS Applications Assistance Facilities. 
You may request a geographic search using any of the three 
following options: 

1. Point search - all images or photographs with any 
portion falling with 50 miles (80 km) of the point will 
be included. 

2. Area rectangle - any area of interest defined by four 
corner coordinates of latitudes and longitudes. All 
images or photographs with any coverage of the area 
will be listed. The area must not exceed 200 one- 
degree squares (for example, 10° latitude by 20° longi- 
tude). 

3. You may enclose a map with a point or area indicated. 

When requesting a geographic search from the Data Center, 
be sure to provide all relevant information. This should include 
acceptable dates and seasons, type of imagery preferred, color, 
false-color infrared, or black-and-white, cloud cover, and quality. 
Cloud cover is given only in percentage, hence no assurance can 
be given as to where clouds will appear on the resulting photo- 
graphs or images. A description of your intended application and 
the use of the data will assist the researcher at the Data Center 
who initiates the search, thereby resulting in a more concise 
response to your inquiry. 

GEOGRAPHIC AREAS MUST BE CLEARLY IDENTIFIED AND SHOULD BE 
LIMITED IN SIZE AS MUCH AS POSSIBLE TO AVOID A POTENTIALLY LONG 
COMPUTER LISTING AND THE NEED TO REVIEW LARGE NUMBERS OF CHOICES. 
LATITUDE AND LONGITUDE COORDINATE SPECIFICATION IS PREFERRED, 
SINCE THIS IS THE METHOD REQUIRED FOR THE COMPUTER GEOGRAPHIC 
SEARCH. 

Specification in degrees and minutes normally provides 
sufficient locations accuracy. (Each degree of latitude or 
longitude is divided into 60 minutes, and each minute into 60 
seconds. One minute of latitude is roughly one mile.) 

The computerized geographic search is made free of charge. 
Allow at least two weeks for the search to be completed and for 
the computer listing to be sent to you for image or photograph 
selection. 



323 



1 .8 Placing An Order 

Orders for reproductions of data from the EROS Data Center 
can be placed by personal visit, telephone, or mail to the Data 
Center. Orders can also be placed at any of the EROS Appli- 
cations Assistance Facilities. 

All orders must be accompanied by check, money order, pur- 
chase order, or authorized account identification; processing 
cannot be initiated until valid and accurate payment is received. 
Your check or money order should be made payable to the U.S. 
Geological Survey. 



324 . 



2.0 OTHER GOVERNMENT AGENCIES 

2.1 U.S. Department of Agriculture 

The Department of Agriculture maintains a distribution 
facility in Salt Lake City, Utah for the reproduction of LANDSAT 
and Skylab imagery. Soil Conservation Service aerial photography, 
and some NASA aerial photography. They will provide free Photo- 
graphic Coverage Status Maps for each state. These maps show the 
scale, date and areal coverage for different photographic missions 
For more specific information, photo indexes can be purchased for 
$5 each. 

The address is: 

Aerial Photography Field Office 

USDA 

2505 Parley's Way 

Salt Lake City, Utah 84109 

Phone: 801-524-5856 



2.2 National Oceanic and Atmospheric Administration 

Weather satellite data, plus LANDSAT and SKYLAB imagery, are 
available through the Environmental Data Service Section of the 
National Oceanic and Atmospheric Administration (NOAA). For 
tunnel siting studies the weather satellite imagery will probably 
be of no value. Computer searches can be made for a printout of 
coverage of specific areas of interest, and orders for LANDSAT 
and Skylab imagery are currently filled in seven to ten days. 



2.3 NOAA Browse File Locations 

NOAA maintains browse files at various locations in the 
country which can be visited to examine the 16 mm film catalogs 
of imagery. 



University of Alaska 

Arctic Environmental Information 

and Data Center 
142 East Third Avenue 
Anchorage, Alaska 99501 
Telephone: 907-279-4523 



Inter-American Tropical Tuna 

Commission 
Scripps Institute of 

Oceanography 
Post Office Box 109 
LaJolla, California 92037 
Telephone: 714-453-2820 



325 



National Geophysical and Solar 

Terrestrial Data Center 
Solid Earth Data Service 

Branch 
Boulder, Colorado 80302 
Telephone: 303-499-1000, 

ext. 6915 

National Oceanographic Data 

Center 
Environmental Data Service 
2001 Wisconsin Avenue 
Washington, D.C. 20235 
Telephone: 202-634-7510 

Atlantic Oceanographic and Meteorological 

Laboratories 
15 Rickenbacker Causeway, Virginia Key 
Miami, Florida 33149 
Telephone: 305-361-3361 

National Weather Service, Pacific Region 
Bethel-Pauaha Building, WFP 3 
1149 Bethel Street 
Honolulu, Hawaii 96811 
Telephone: 808-841-5028 

National Ocean Survey - C3415 
Building #1, Room 526 
6001 Executive Boulevard 
Rockville, Maryland 20852 
Telephone: 301-443-8601 

Atmospheric Sciences Library - D821 

Gramax Building, Room 816 

8060 13th Street 

Silver Spring, Maryland 20910 

Telephone: 301-427-7800 

National Environmental Satellite Service 
Environmental Sciences Group 
Suitland, Maryland 20233 
Telephone: 301-763-5981 

Northeast Fisheries Center 
Post Office Box 6 
Woods Hole, Massachusetts 02543 
Telephone: 617-548-5123 



Lake Survey Center - CLxl3 
630 Federal Building & U.S. 

Courthouse 
Detroit, Michigan 48226 
Telephone: 313-226-6126 

National Weather Service, 

Central Region 
601 East 12th Street 
Kansas City, Missouri 64106 
Telephone: 816-374-5672 

National Weather Service, 

Eastern Region 
585 Stewart Avenue 
Garden City, New York 11530 
Telephone: 516-248-2105 

National Climatic Center 
Federal Building 
Asheville, North Carolina 

28801 
Telephone: 704-258-2850, 

ext. 620 

National Severe Storms Lab 
1313 Hal ley Circle 
Norman, Oklahoma 73069 
Telephone: 405-329-0388 

Remote Sensing Center 
Texas A & M University 
College Station, Texas 77843 
Telephone: 713-845-5422 



National Weather Service, 

Southern Region 
819 Taylor Street 
Fort Worth, Texas 76102 
Telephone: 817-334-2671 

National Weather Service, 

Western Region 
125 South State Street 
Salt Lake City, Utah 84111 
Telephone: 801-524-5131 



326 



Atlantic Marine Center - CAM02 
439 West York Street 
Norfolk, Virginia 23510 
Telephone: 804-441-6201 

Northwest Marine Fisheries 

Center 
2725 Montlake Boulevard East 
Seattle, Washington 98112 
Telephone: 206-442-4760 



University of Wisconsin 
Office of Sea Grant 
610 North Walnut Street 
Madison, Wisconsin 53705 
Telephone: 608-263-4836 



2.4 National Ocean Survey 

The National Ocean Survey (NOS) has substantial quantities 
of aerial photography of areas immediately adjacent to the coast- 
line of the United States. The scale of aerial photographic 
reproduction is secondary to the National Ocean Survey's res- 
ponsibility for charting. Normally, outside orders will be 
filled in less than 30 days but official charting requirements 
will be given priority. The requester should describe the 
specific area of interest by geographic coordinates, a detailed 
description or a sketch. (See discussion below on PHOTO INDEX 
SHEETS.) 

Payment by check, money order, or draft, payable to National 
Ocean Survey, Commerce Department, shall accompany orders. No 
discount is offered for quantity purchases. 

Prints are not stocked. They are custom processed for each 
order and cannot be returned for credit or refund. This includes 
mis-ordered prints. 

Shipment by parcel post is pre-paid. Shipment by express, 
airmail, or involving special handling must be paid for by the 
purchaser. 

Authorization to purchase photographs of classified areas 
must be obtained by the purchaser from appropriate military 
authorities. This office will inform the requester when such 
clearance is required and how to submit the application. 

National Ocean Survey aerial photography is of a single lens 
type, some panchromatic, some color and a smaller portion of 
black-and-white infrared and false-color infrared. 

Single lens aerial photographs are usually exposed at scales 
from 1:10,000 to 1:40,000. 



327 



The National Ocean Survey's aerial photography is special 
purpose photography. Usually it consists of a single strip or a 
few parallel strips of photographs. It is impracticable to index 
this photography by the single mosaic method commonly used by 
other government agencies. 

The photographs are usually indexed on 1:250,000 scale base 
maps that cover an area of 1° of latitude by 1° of longitude with 
each individual exposure indicated by a dot. Occasionally, 
larger scale bases are used for indexes. Separate series of 
photo indexes are maintained for the different categories of 
photography as follows: 

Panchromatic, black-and-white infrared, natural color, and 
false-color infrared. 

Diazo prints of indexes are available at $.50 each upon 
request. For further information or to place an order, contact: 

Coastal Mapping Division C3415 
National Ocean Survey, NOAA 
6001 Executive Blvd. 
Rockville, Md. 20852 
Phone: 301-443-8601 



328 



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